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111.
Sthefane D’ávila Camilla Medeiros Tércia Vargas Cristiane Lafetá Furtado Mendonça 《Journal of Natural History》2018,52(23-24):1551-1569
In the present study, we aimed to characterize the life history of the land snail Subulina octona integrating information on life-history traits and morphology. We also compared the histology of the free-oviduct and spermoviduct of ovoviviparous and egg-retaining species of subulinids. We considered as ovoviviparous the species in which the complete embryonic development as well as egg hatching occurs inside the parent’s body and, at the end of this process, the parent releases juveniles instead of eggs. We considered as egg-retaining the species in which a great part of the embryonic development takes place inside the parent’s body and the eggs laid contain well-developed embryos. The results showed that the free-oviduct of both ovoviviparous and egg-retaining species shows a histological arrangement that confers greater strength to its walls and is probably related to egg retention. The wall of the spermoviduct is formed by pseudostratified columnar epithelium, with cell apical processes (probably cilia), and by underlying secretory cells. In gravid egg-retaining snails, the eggshells appear in close contact with the secretory cells of the spermoviduct. This fact suggests that these cells play a role in eggshell formation. The present study is the first account for histological features of S. octona, Allopeas gracile and Allopeas micra. The life history of S. octona is a combination of long lifespan, early sexual maturity, indeterminate growth and egg retention. Egg retention limits the number of young that can be produced in one reproductive event. However, the reproductive strategy adopted by S. octona, associating egg retention and K-strategism, compensates this cost of retaining eggs, because the reproductive success may be enhanced as a result of the higher survival of juveniles and the possibility of performing several reproductive events during the year. 相似文献
112.
G. Mathé P. Pouillart Françoise Lapeyraque 《Cellular and molecular life sciences : CMLS》1971,27(4):446-447
Résumé L'immunothérapie active non spécifique ou mixte, appliquée 24 h après la greffe isogénique de la leucémie RC 19, possède une action considérable; appliquée dans les mêmes conditions après la greffe de la leucémie E K1, elle possède une action modérée mais significative. Ces résultats confirment l'effet antileucémique de l'immunothérapie active appliquée après le début de la maladie et montre qu'elle est même efficace sur les cellules tumorales disséminées.
This work has been carried out with the aid of INSERM, contract No. 66-235. 相似文献
This work has been carried out with the aid of INSERM, contract No. 66-235. 相似文献
113.
114.
Maria Luiza Beçak Sylvia Mendes Carneiro K. Fukuda 《Cellular and molecular life sciences : CMLS》1978,34(2):171-173
Summary We describe the production of circles in chromomeric loops during the pachytene stage of the spermatocytes. These circles are found attached to chromatin or already free in the nucleoplasm. Each circle measures an average of 3700 Å in circunference. We suggest that such circles might indicate the presence of tandem repetitions.This work was supported by grants from Brazilian National Research Council-CNPq, Fundaçaó de Amparo à Pesquisa do Estado de S. Paulo-FAPESP and Instituto Butantan Research Found-FEDIB.We are grateful to Dr A. Brunner, Jr, for the permission to use the electron microscope. 相似文献
115.
A. S. Etienne J. Vauclair E. Emmanuelli M. Lançon J. Stryjenski 《Cellular and molecular life sciences : CMLS》1982,38(5):553-555
Summary Golden hamsters placed on a jumping stand from which they can descend onto a shallow or deep landing platform prefer to descend
on to the shallow platform, even when tested under IR-light without tactile cues. This preference disappears for subjects
with plugged ears. The simultaneous recording of the animal's behaviour and possible emission of ultrasound as well as experiments
in which the external acoustical conditions or the sound-reflecting properties of the jumping apparatus were altered suggest
that the animals use certain parameters of the ambient sound field for depth perception.
Acknowledgments. This research was supported by the Fonds National Suisse de la Recherche Scientifique, grant No. 3.349.74. 相似文献
116.
J. Diézi Françoise Roch-Ramel Françoise Chométy Pierrette Michoud G. Peters 《Cellular and molecular life sciences : CMLS》1969,25(9):932-933
Summary The renal tubular fate of urea, as studied in the rat by free-flow micropunctures of cortical tubules, is shown to vary with different types of diuresis (urea overloading, iso- or hypertonic saline diuresis). Under certain experimental conditions, the renal tubular handling of urea appears to differ in the cortical and the juxtamedullary nephrons.
Ce travail bénéficie du soutien du Fond National suiss de la Recharche Scientifique (crédit Nos. 4495 et 4983). 相似文献
Ce travail bénéficie du soutien du Fond National suiss de la Recharche Scientifique (crédit Nos. 4495 et 4983). 相似文献
117.
An updatable holographic three-dimensional display 总被引:2,自引:0,他引:2
Tay S Blanche PA Voorakaranam R Tunç AV Lin W Rokutanda S Gu T Flores D Wang P Li G St Hilaire P Thomas J Norwood RA Yamamoto M Peyghambarian N 《Nature》2008,451(7179):694-698
Holographic three-dimensional (3D) displays provide realistic images without the need for special eyewear, making them valuable tools for applications that require situational awareness, such as medical, industrial and military imaging. Currently commercially available holographic 3D displays use photopolymers that lack image-updating capability, resulting in restricted use and high cost. Photorefractive polymers are dynamic holographic recording materials that allow updating of images and have a wide range of applications, including optical correlation, imaging through scattering media and optical communication. To be suitable for 3D displays, photorefractive polymers need to have nearly 100% diffraction efficiency, fast writing time, hours of image persistence, rapid erasure, and large area-a combination of properties that has not been shown before. Here, we report an updatable holographic 3D display based on photorefractive polymers with such properties, capable of recording and displaying new images every few minutes. This is the largest photorefractive 3D display to date (4 x 4 inches in size); it can be recorded within a few minutes, viewed for several hours without the need for refreshing, and can be completely erased and updated with new images when desired. 相似文献
118.
Andäng M Hjerling-Leffler J Moliner A Lundgren TK Castelo-Branco G Nanou E Pozas E Bryja V Halliez S Nishimaru H Wilbertz J Arenas E Koltzenburg M Charnay P El Manira A Ibañez CF Ernfors P 《Nature》2008,451(7177):460-464
Stem cell self-renewal implies proliferation under continued maintenance of multipotency. Small changes in numbers of stem cells may lead to large differences in differentiated cell numbers, resulting in significant physiological consequences. Proliferation is typically regulated in the G1 phase, which is associated with differentiation and cell cycle arrest. However, embryonic stem (ES) cells may lack a G1 checkpoint. Regulation of proliferation in the 'DNA damage' S/G2 cell cycle checkpoint pathway is known for its role in the maintenance of chromatin structural integrity. Here we show that autocrine/paracrine gamma-aminobutyric acid (GABA) signalling by means of GABA(A) receptors negatively controls ES cell and peripheral neural crest stem (NCS) cell proliferation, preimplantation embryonic growth and proliferation in the boundary-cap stem cell niche, resulting in an attenuation of neuronal progenies from this stem cell niche. Activation of GABA(A) receptors leads to hyperpolarization, increased cell volume and accumulation of stem cells in S phase, thereby causing a rapid decrease in cell proliferation. GABA(A) receptors signal through S-phase checkpoint kinases of the phosphatidylinositol-3-OH kinase-related kinase family and the histone variant H2AX. This signalling pathway critically regulates proliferation independently of differentiation, apoptosis and overt damage to DNA. These results indicate the presence of a fundamentally different mechanism of proliferation control in these stem cells, in comparison with most somatic cells, involving proteins in the DNA damage checkpoint pathway. 相似文献
119.
Carbonic anhydrase, a zinc enzyme found in organisms from all kingdoms, catalyses the reversible hydration of carbon dioxide and is used for inorganic carbon acquisition by phytoplankton. In the oceans, where zinc is nearly depleted, diatoms use cadmium as a catalytic metal atom in cadmium carbonic anhydrase (CDCA). Here we report the crystal structures of CDCA in four distinct forms: cadmium-bound, zinc-bound, metal-free and acetate-bound. Despite lack of sequence homology, CDCA is a structural mimic of a functional beta-carbonic anhydrase dimer, with striking similarity in the spatial organization of the active site residues. CDCA readily exchanges cadmium and zinc at its active site--an apparently unique adaptation to oceanic life that is explained by a stable opening of the metal coordinating site in the absence of metal. Given the central role of diatoms in exporting carbon to the deep sea, their use of cadmium in an enzyme critical for carbon acquisition establishes a remarkable link between the global cycles of cadmium and carbon. 相似文献
120.
Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years 总被引:3,自引:0,他引:3
Kawamura K Parrenin F Lisiecki L Uemura R Vimeux F Severinghaus JP Hutterli MA Nakazawa T Aoki S Jouzel J Raymo ME Matsumoto K Nakata H Motoyama H Fujita S Goto-Azuma K Fujii Y Watanabe O 《Nature》2007,448(7156):912-916
The Milankovitch theory of climate change proposes that glacial-interglacial cycles are driven by changes in summer insolation at high northern latitudes. The timing of climate change in the Southern Hemisphere at glacial-interglacial transitions (which are known as terminations) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis. So far, it has only been possible to apply this test to the most recent termination, because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined. Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores. This ratio is a proxy for local summer insolation, and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter. The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation. Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia, and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation. These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations. 相似文献