全文获取类型
收费全文 | 47324篇 |
免费 | 140篇 |
国内免费 | 222篇 |
专业分类
系统科学 | 242篇 |
丛书文集 | 857篇 |
教育与普及 | 74篇 |
理论与方法论 | 175篇 |
现状及发展 | 21881篇 |
研究方法 | 1826篇 |
综合类 | 21859篇 |
自然研究 | 772篇 |
出版年
2013年 | 376篇 |
2012年 | 655篇 |
2011年 | 1411篇 |
2010年 | 286篇 |
2008年 | 806篇 |
2007年 | 941篇 |
2006年 | 907篇 |
2005年 | 897篇 |
2004年 | 956篇 |
2003年 | 815篇 |
2002年 | 844篇 |
2001年 | 1354篇 |
2000年 | 1303篇 |
1999年 | 923篇 |
1992年 | 872篇 |
1991年 | 642篇 |
1990年 | 727篇 |
1989年 | 726篇 |
1988年 | 690篇 |
1987年 | 757篇 |
1986年 | 755篇 |
1985年 | 956篇 |
1984年 | 731篇 |
1983年 | 591篇 |
1982年 | 545篇 |
1981年 | 576篇 |
1980年 | 703篇 |
1979年 | 1497篇 |
1978年 | 1233篇 |
1977年 | 1176篇 |
1976年 | 961篇 |
1975年 | 984篇 |
1974年 | 1379篇 |
1973年 | 1199篇 |
1972年 | 1264篇 |
1971年 | 1389篇 |
1970年 | 1843篇 |
1969年 | 1454篇 |
1968年 | 1363篇 |
1967年 | 1343篇 |
1966年 | 1202篇 |
1965年 | 867篇 |
1964年 | 304篇 |
1959年 | 471篇 |
1958年 | 847篇 |
1957年 | 597篇 |
1956年 | 491篇 |
1955年 | 452篇 |
1954年 | 497篇 |
1948年 | 319篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Flesher MM 《Annals of science》1997,54(5):463-487
The addition of 'fire' to the European battle repertoire resulted in the close-order drill for manoeuvres of the line. Begun in late sixteenth-century Netherlands and perfected in eighteenth-century Prussia under Frederick the Great, the drill's precision marching evolved into a military science which conceived what infantry acquired through rigorous training as a lawful 'second nature' of men. In contrast, the liberal Webers' 1836 locomotion research orientation was, as was that of French skirmishing, one of natural self-regulation. Later Prussian military science, restored in Imperial Germany, was merged into locomotion science. 相似文献
232.
S. Fujino K. Satoh T. Nakai K. Togashi T. Kado M. Fujino T. Arima M. Fujino 《Cellular and molecular life sciences : CMLS》1993,49(2):138-144
The excitation-contraction (E-C) coupling process in single twitch fibres from frog toe muscle was inhibited selectively by phenylglyoxal (PGO), a specific guanidyl modifying reagent. A new protein (31.5 kDa), which has PGO-binding ability and seems to play a key role in the E-C coupling process, was solubilized from transverse tubule membrane-junctional sarcoplasmic reticulum complexes (TTM-JSR) of frog skeletal muscles, using14C-PGO. The monoclonal antibody against this protein applied extracellularly inhibited the E-C coupling process of the single fibres. This protein appears to constitute the very first step of input for E-C coupling. It is considered to behave as an indispensable part of an electrometer to measure membrane potentials. Therefore, the name electrometrin is suggested for the new protein. 相似文献
233.
M. Kates 《Cellular and molecular life sciences : CMLS》1993,49(12):1027-1036
Archaebacteria (archaea) are comprised of three groups of prokaryotes: extreme halophiles, methanogens and thermoacidophiles (extreme thermophiles). Their membrane phospholipids and glycolipids are derived entirely from a saturated, isopranoid glycerol diether,sn-2,3-diphytanylglycerol (archaeol) and/or its dimer, dibiphytanyldiglyceroltetraether (caldarchaeol). In extreme halophiles, the major phospholipid is the archaeol analogue of phosphatidylglycerolmethylphosphate (PGP-Me); the glycolipids are sulfated and/or unsulfated glycosyl archaeols with diverse carbohydrate structure characteristic of taxons on the generic level. Biosynthesis of these archaeol-derived polar lipids occurs in a multienzyme, membrane-bound system that is absolutely dependent on high salt concentration (4 M). The highly complex biosynthetic pathways involve intermediates containing glycerol ether-linked C20-isoprenyl groups which are reduced to phytanyl groups to give the final saturated polar lipids. In methanogens, polar lipids are derived both from archaeol and caldarchaeol, and thermoacidophiles contain essentially only caldarchaeol-derived polar lipids. The function of these membrane polar lipids in maintaining the stability, fluidity and ionic properties of the cell membrane of extreme halophiles, as well as the evolutionary implications of the archaeol and caldarchaeol-derived structures will be discussed. 相似文献
234.
The Black Sea is the world's largest anoxic basin; it is also a contemporary analogue of the environment in which carbonaceous shales and petroleum source beds formed. Recently, Repeta et al. reported that anoxygenic photosynthesis may be an important component of carbon cycling in the present Black Sea, owing to a shoaling of the chemocline and consequent penetration of the photic zone by anaerobic waters in the past few decades. It has been suggested that this was due to an anthropogenic decrease in freshwater input to the Black Sea, although natural causes were not ruled out. Here we report the distributions of sequestered photosynthetic pigments in eight core samples of sediments from the Black Sea ranging in age from zero to 6,200 years before the present. Our results show that photosynthetic green sulphur bacteria (Chlorobiaceae [correction of Clorobiaceae]) have been active in the Black Sea for substantial periods of time in the past. This finding indicates that the penetration of the photic zone by anaerobic waters is not a recent phenomenon, and suggests that natural causes for shoaling of the chemocline are more likely than anthropogenic ones. 相似文献
235.
M. Rizzardini A. Ferraroli D. Dal Fiume L. Cantoni 《Cellular and molecular life sciences : CMLS》1984,40(12):1390-1392
Summary Im male rats hepatic cytochromes b5 and P-450 were reduced at different times after treatment with cyclophosphamide (CP) (200 mg/kg i.p. for 3 days). In contrast, microsomal heme did not change until 48 h after the last dose of CP, leading to accumulation of heme in a non-cytochromal form. Parallel to the above changes the heme metabolism showed derangement: -aminolaevulinate synthase, the rate-limiting enzyme in heme synthesis, was depressed and heme oxygenase, the enzyme which catalyzes the oxidative degradation of heme, was increased. 相似文献
236.
E. A. Morguenstern M. I. Vacas M. I. Keller Sarmiento D. P. Cardinali 《Cellular and molecular life sciences : CMLS》1984,40(2):223-224
Summary Pinealectomy (Px) in adult male rats resulted in increased cyclic AMP accumulation by medial basal hypothalamic (MBH) explants 3 and 7 days after surgery. 24 h after superior cervical ganglionectomy (Gx) an augmented MBH cyclic AMP accumulation was observed. The effects of Px and Gx were additive, as revealed in animals subjected to Gx 3 days after Px.This study was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (No 6638) and from the Fundación Alberto J. Roemmers, Argentina. 相似文献
237.
Ph. van den Bosch de Aguilar Ch. Langhendries-Wéverberg J. Goemaere-Vanneste F. Flament-Durand J. P. Brion A. M. Couck 《Cellular and molecular life sciences : CMLS》1984,40(4):402-403
Summary Senile dementia of the Alzheimer type (SDAT) is a major problem in the human senescent population. As this pathology cannot be reproduced in animals, research into its development is greatly impeded. The technique of implantation of the nervous tissue has been utilized in order to establish an animal model and to test the possible existence of a transmissible agent. When human temporal cortex with Alzheimer's disease is implanted in the occipital cortex of 7-week-old rats, human cerebral tissue containing abundant tangles induces in the receiver cortex a reactive fibrous gliosis. In the processes of the astrocytes, twisted filaments are evident among bundles of normal filaments. These alterations could be induced by the metabolising of abnormal filament subunits or by some infectious agent introduced by the implant.This study is supported by grant No. 2.4517.82 of Fonds de la Recherche Fondamentale Collective of Belgium. 相似文献
238.
239.
F. M. Goñi J. M. Valpuesta M. C. Barbero E. Rial J. I. G. Gurtubay J. M. Macarulla 《Cellular and molecular life sciences : CMLS》1984,40(2):193-195
Summary The solubilizing effect of Triton X-100 on beef heart submitochondrial particles (ETPH) has been studied under various physiological conditions. Coupled, uncoupled and azide-inhibited ETPH particles have been studied. Quantitative and qualitative differences are found in the proteins solubilized by the detergent from ETPH particles under the various conditions tested.Acknowledgments: This work was supported in part by a grant from a Spanish Comisión Asesora para la Investigación Cientifica y Técnica. M.C. Barbero was recipient of a scholarship from the Basque Government. 相似文献
240.
Summary The cuticle from adultGaigeria pachyscelis was isolated by solubilizing the internal tissues with sodium dodecyl sulphate (SDS) at 37°C. Cuticular protein was extracted with guanidine-HCl and -mercaptoethanol and purified by ammonium sulphate fractionation and DEAE-cellulose chromatography. SDS-polyacrylamide gel electrophoresis of purified protein revealed 2 polypeptides with apparent mol. wts of 58,000 and 74,000. As judged from their hydroxyproline content both of them are collagenous in nature. Results of gel filtration indicate that cuticular collagen exists in two forms, a non-associated form at low concentration and an associated form at high concentration.Acknowledgments. We thank Drs L.N. Singh and H.C. Tewari for providing the necessary facilities. Laboratory assistance of Mr Ram Kishore is highly appreciated. 相似文献