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211.
U. Graf 《Cellular and molecular life sciences : CMLS》1995,51(2):168-173
The relationship between the induction of mutant clones and the time of mutagen treatment was studied in the somatic mutation and recombination test (SMART) in wing cells ofDrosophila melanogaster. Larvae trans-heterozygous for the recessive marker mutations multiple wing hairs (mwh) and flare (flr) were produced. Batches of these larvae were then treated with mutagen at different ages spanning all three larval instars. Methyl methanesulfonate was fed acutely for 2 h by immersing the larvae in a solution of the mutagen mixed with powdered cellulose. Wings of the surviving adult flies were mounted and scored for the presence of spots. The frequency and size of single and twin spots were recorded separately. Twin spots are produced exclusively by mitotic recombination, whereas single spots can results from various types of mutational and exchange events. There exists a clear correlation between time of induction and frequency as well as size of the single spots. In young larvae only few but very large spots are induced, whereas in older larvae the frequencies are considerably increased but the sizes are smaller. The twin spots show a different relationship. Practically no twin spots are found in very young and in very old larvae. The results demonstrate that in the wing spot test the optimal age of the larvae for mutagen treatment is 72 h. 相似文献
212.
AIDS virus-specific cytotoxic T lymphocytes in lung disorders 总被引:6,自引:0,他引:6
F Plata B Autran L P Martins S Wain-Hobson M Rapha?l C Mayaud M Denis J M Guillon P Debré 《Nature》1987,328(6128):348-351
Human immunodeficiency virus (HIV) is implicated in the development of AIDS (acquired immune deficiency syndrome). HIV infection leads to the generation of HIV-specific thymus-derived (T) lymphocytes in humans and apes. We describe an experimental system permitting the quantitative and systematic analysis of HIV-specific cytotoxic T lymphocytes (CTL). Functional, HIV-specific CTL are obtained by broncho-alveolar lavage (BAL) from the lungs of seropositive patients with lymphocytic alveolitis. These alveolar CTL: (1) recognize and kill HIV-infected alveolar macrophages in vitro under autologous, but not heterologous, conditions; (2) correspond to standard CTL as they express the CD3 and CD8 surface markers, but not the CD4 marker; and (3) are restricted by class I HLA transplantation antigens in their cytotoxic activities. We propose the hypothesis that interactions between HIV-specific CTL and infected macrophages induce major inflammatory reactions in seropositive patients. 相似文献
213.
Microtubules are versatile cellular polymers that play a role in cell shape determination and mediate various motile processes such as ciliary and flagellar bending, chromosome movements and organelle transport. That a sliding microtubule mechanism can generate force has been demonstrated in highly ordered structures such as axonemes, and microtubule-based force generation almost certainly contributes to the function of mitotic and meiotic spindles. Most cytoplasmic microtubule arrays, however, do not exhibit the structural regularity of axonemes and some spindles, and often appear disorganized. Yet many cellular activities (such as shape changes during morphogenesis, axonal extension and spindle assembly) involve highly coordinated microtubule behaviour and possibly require force generated by an intermicrotubule sliding mechanism, or perhaps use sliding to move microtubules rapidly into a protrusion for stabilization. Here we show that active sliding between cytoplasmic microtubules can occur in microtubule bundles of the amoeba Reticulomyxa. A force-producing mechanism of this sort could be used by this organism to facilitate the extension of cell processes and to generate the dynamic movements of the cytoplasmic network. 相似文献
214.
Plant thioredoxins: the multiplicity conundrum 总被引:4,自引:0,他引:4
Thioredoxins are small proteins distinguished by the presence of a conserved dicysteine active site. In oxidized thioredoxin,
the two cysteines form a disulfide bond that is targeted by the enzyme thioredoxin reductase. Together with an electron donor,
thioredoxin and thioredoxin reductase form the 'thioredoxin system' that is present in all organisms. Thioredoxins participate
in dithiol/disulfide exchange reactions with a large range of cellular substrates. Higher plants possess a very complex thioredoxin
profile consisting of at least two different thioredoxin systems that contain distinct, multigenic thioredoxin classes which
have different intracellular localizations. In this review we summarise the current state of knowledge regarding the function
of plant thioredoxins representing all systems and classes.
Received 30 October 2001; received after revision 13 December 2001; accepted 17 December 2001 相似文献
215.
Wabnitz H Bittner L de Castro AR Döhrmann R Gürtler P Laarmann T Laasch W Schulz J Swiderski A von Haeften K Möller T Faatz B Fateev A Feldhaus J Gerth C Hahn U Saldin E Schneidmiller E Sytchev K Tiedtke K Treusch R Yurkov M 《Nature》2002,420(6915):482-485
Intense radiation from lasers has opened up many new areas of research in physics and chemistry, and has revolutionized optical technology. So far, most work in the field of nonlinear processes has been restricted to infrared, visible and ultraviolet light, although progress in the development of X-ray lasers has been made recently. With the advent of a free-electron laser in the soft-X-ray regime below 100 nm wavelength, a new light source is now available for experiments with intense, short-wavelength radiation that could be used to obtain deeper insights into the structure of matter. Other free-electron sources with even shorter wavelengths are planned for the future. Here we present initial results from a study of the interaction of soft X-ray radiation, generated by a free-electron laser, with Xe atoms and clusters. We find that, whereas Xe atoms become only singly ionized by the absorption of single photons, absorption in clusters is strongly enhanced. On average, each atom in large clusters absorbs up to 400 eV, corresponding to 30 photons. We suggest that the clusters are heated up and electrons are emitted after acquiring sufficient energy. The clusters finally disintegrate completely by Coulomb explosion. 相似文献
216.
217.
Jian?Zhang Sumin?Li Yongqiang?Tian Yunge?Zhao Amy?Sang?Qing-Xiang Enkui?DuanEmail author 《科学通报(英文版)》2002,47(22):1884-1888
Matrix metalloproteinase-26 (MMP-26, endometase and matrilysin-2), a novel member of the MMPs family, is detected not only
in the placenta and uterus, but is widely expressed in malignant tumors from different sources as well as in diverse tumor
cell lines. However, the function of MMP-26 in the reproductive system has never been reported. Expression of MMP-26 in mouse
embryos and the function of the MMP-26 antibody during mouse embryo implantation was examined for the first time by injecting
the uterine horn, immunohistochemistry,in situ hybridization, co-culture of mouse blastocysts and uterine monolayer epithelial cells, Western blot, RT-PCR, Northern blot
and zymography. Our results show that there is strong expression of MMP-26 mRNA and protein in the mouse embryo. Furthermore,
the MMP-26 antibody dramatically inhibited mouse embryo implantation and significantly inhibited adhesion and outgrowth of
mouse blastocysts onin vitro uterine monolayer epithelial cells. At the same time, the MMP-26 antibody inhibited the expression of integrin αV mRNA and
protein in a dose-dependent manner. These data suggest that MMP-26 may play a role in some of the tissue-remodeling events
associated with the invasion of the endometrium by trophoblast cells and facilitate successfully embryo implantation. 相似文献
218.
Cunyue?Guo Zhi?Ma Mingge?Zhang Aihua?He Yucai?Ke Youliang?HuEmail author 《科学通报(英文版)》2002,47(15):1267-1270
The catalyst [(2-ArN=C(Me))2C5H3N]FeCl2 (Ar = 2-C6H4(i-Pr)) with methylaluminoxane (MAO) as cocatalyst was intercalated between layers of montmorillonite (MMT) for ethylene oligomerization.
Metallocene catalyst Me2Si(Ind)2ZrCl2 and MAO was then added to form a dual functional catalytic system. A PE/MMT nanocomposite was prepared by copolymerization
of ethylene with α-olefins produced in situ from ethylene over the dual functional catalytic system. The catalytic system was of high polymeric activity. The resultant
PE/MMT nanocomposites were stable and got increases in tensile strength and temperature of maximum weight loss (Tonset). 相似文献
219.
Radiolarian record to paleoecological environment change events over the past 1.2 MaBP in the southern South China Sea 总被引:2,自引:0,他引:2
This note studies the Radiolarian fossil groups since 1.2 MaBP in ODP leg 184 site 1143, the southern South China Sea (SCS).
The result shows that radiolarian abundance experienced a significant variation: before 0.9 MaBP it remained at the extremely
low level, but increased with low extent between 0.9–0.65 Ma, which corresponded to the Mid-Pleistocene Transition stage,
and it increased rapidly after 0.65 MaBP. During the whole process, the average abundance became higher and higher in each
stage, and showed regularly periodic fluctuations. The obvious increase after 0.65 MaBP is inferred to result from the enhanced
upwelling in this region, which was induced by the intensified monsoon circulation after the “Mid-Pleistocene Transition”.
An outstanding result of the spectral analyses is that a long oscillation of ∼ 0.2 Ma cycle was found in the records of radiolarian
abundance and complex diversity, which corresponds well to the result of other paleoceanographic indexes. This probably indicated
a special cycle characteristic of paleoecological environment evolution in this area. In addition, all of the radiolarian
indexes show an obvious boundary in about 0.47 MaBP, indicating the abrupt variation of the community structure and radiolarian
abundance level before and after 0.47 MaBP. So we suppose that there existed a distinct change event of oceanic ecology environment
during that period. 相似文献
220.
The intron is an important component of eukaryotic gene. Extensive studies have been conducted to get a better understanding
of its structure and function. This paper presents a brief review of the structure and function of introns in higher plant
genes. It is shown that higher plant introns possess structural properties shared by all eukaryotic introns, however, they
also exhibit a striking degree of diversity. The process of intron splicing in higher plant genes involves interaction between
multiple cis-acting elements and trans-acting factors, such as 5′ splicing site, 3′ splicing site and many protein factors. The process of intron splicing is an
important level at which gene expression is regulated. Especially alternative splicing of intron can regulate time and space
of gene expression. In addition, some introns in higher plant genes also regulate gene expression by affecting the pattern
of gene expression, enhancing the level of gene expression and driving the gene expression. 相似文献