全文获取类型
收费全文 | 10227篇 |
免费 | 554篇 |
国内免费 | 351篇 |
专业分类
11132篇 |
出版年
2023年 | 155篇 |
2022年 | 216篇 |
2021年 | 251篇 |
2020年 | 261篇 |
2019年 | 299篇 |
2018年 | 336篇 |
2017年 | 201篇 |
2016年 | 235篇 |
2015年 | 309篇 |
2014年 | 486篇 |
2013年 | 611篇 |
2012年 | 350篇 |
2011年 | 569篇 |
2010年 | 463篇 |
2009年 | 591篇 |
2008年 | 547篇 |
2007年 | 539篇 |
2006年 | 486篇 |
2005年 | 477篇 |
2004年 | 407篇 |
2003年 | 305篇 |
2002年 | 295篇 |
2001年 | 207篇 |
2000年 | 180篇 |
1999年 | 186篇 |
1998年 | 163篇 |
1997年 | 137篇 |
1996年 | 120篇 |
1995年 | 125篇 |
1994年 | 126篇 |
1993年 | 110篇 |
1992年 | 99篇 |
1991年 | 82篇 |
1990年 | 82篇 |
1989年 | 92篇 |
1988年 | 62篇 |
1987年 | 60篇 |
1986年 | 52篇 |
1985年 | 65篇 |
1984年 | 146篇 |
1983年 | 108篇 |
1982年 | 107篇 |
1981年 | 93篇 |
1980年 | 81篇 |
1979年 | 59篇 |
1978年 | 37篇 |
1977年 | 40篇 |
1976年 | 26篇 |
1975年 | 28篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
Mario De Rosa Agata Gambacorta Barbara Nicolaus Salvatore Sodano J.D. BuLock 《Phytochemistry》1980,19(5):833-836
Individual di(biphytanyl) diglycerol tetraether lipids from thermoacidophile archaebacteria of the Caldariella series, with differently cyclized biphytanyl components, are separated and shown to have structures 8–12, with the glycerol and biphytanyl components demonstrably both antiparallel and with partial assignments of stereochemistry. Tetraethers with alternative arrangements of the components are absent. The structures allow previous observations on these and related lipids to be rationalized both biosynthetically and phyletically. 相似文献
43.
44.
Sensitivity of CaMg ATPase from axonic plasma membrane (APM) and sarcoplasmic reticulum (SR) of lobster, , to DDT was studied. The CaMg ATPase found in SR with the high Ca2+ affinity is sensitive to DDT while the portion of ATPase related to the low Ca2+ affinity site is not inhibited by DDT. Also, DDT is more inhibitory against the CaMg ATPase prepared from APM than the one obtained from SR. The relationship between inhibition of the CaMg ATPase by DDT in the axonic nerve membrane and poisoning symptoms of the nervous system is discussed. 相似文献
45.
Linkage of Pgm-3 in the house mouse and homologies of three phosphoglucomutase loci in mouse and man
The discovery of a third phosphoglucomutase locus (Pgm-3) in the house mouse is reported. Three alleles are recognized on the basis of differences in electrophoretic mobility and enzymatic activity. Pgm-3
a (fast mobility and high activity) is present in inbred strain C57BL/10J and 24 other strains; Pgm-3
b (slow mobility and high activity) is present in LP/Pas and six other strains; and Pgm-3
c (no detectable activity in any tissue tested) is present in strain DBA/2J and 14 other strains. Seventy-four recombinant inbred strains derived from progenitors that differed at Pgm-3 were used to study genic linkage. Pgm-3 is on chromosome 9 and is linked to Sep-1, d, Mod-1, and Ltw-3. Gene order and recombination frequencies are estimated as d 3.8±1.8% Pgm-3 2.3±1.2% Mod-1. Substrate specificities and cofactor requirements show that mouse Pgm-1 is homologous with human Pgm-2, mouse Pgm-2 with human Pgm-1, and mouse Pgm-3 with human Pgm-3.This research was supported in part by NIH Research Grant GM18684 from the National Institute of General Medical Sciences to B.A.T. and by grants from NIH A105531-02 and the Volkswagon Foundation to Jan Klein. J.H.N. was a recipient of a Fellowship from the Max-Planck-Gesellschaft, Munich. G.S. and J.K. were supported by funds from the Deutsche Forschungsgemeinschaft. 相似文献
46.
An isolated light-harvesting pigment-protein complex contains polypeptides which bind chlorophyll a and b. The individual complexes can be purified from detergent-solubilized membranes. The isolated light-harvesting complex, when dialyzed to remove detergents, was examined by freeze-fracture electron microscopy. The material consisted of planar sheets of 80-Å subunits which interacted via an edge-to-edge contact. Addition of cations caused the planar light-harvesting complex sheets to become tightly appressed in multilamellar stacks, with distinct subunits still visible within each lamellar sheet. A transition of particle organization from random to crystalline occurred in parallel with the cation-induced lamellar association. Treatment of the dialyzed light-harvesting complex subunits with low levels of the proteolytic enzyme trypsin removed a 2000 molecular weight segment of the major polypeptide of the light-harvesting complex and blocked all subsequent cation-induced changes in structural organization of the isolated light-harvesting complex lamellar sheets.To gain further evidence for mechanisms of cation effects upon the organization of the light-harvesting complex in native membranes, the light-harvesting complex was incorporated into uncharged (phosphatidylcholine) lipid vesicles. The protein complexes spanned the lipid bilayer and were arranged in either a random pattern or in hexagonal crystalline lattices. Addition of either monovalent or divalent cations to ‘low-salt’ (20 mM monovalent cation) vesicles containing light-harvesting complex caused extensive regions of membrane appression to appear. It is concluded that this cation-induced membrane appression is mediated by surface-exposed segments of the light-harvesting complex since (a) phosphatidylcholine vesicles themselves did not undergo cation-induced aggregation, and (b) mild trypsin digestion of the surface-exposed regions of the light-harvesting complex blocked cation-induced lamellar appression. The particles in the appressed vesicle membranes tended to form long, linear arrays of particles, with occasional mixed quasi-crystalline arrays with an angular displacement near 72°. Surface-mediated interactions among light-harvesting complex subunits of different membranes are, therefore, related to changes in structural organization and interaction of the particles within the lipid phase of the membrane.Numerous previous studies have implicated the involvement of the light-harvesting complex in mediating grana stocking in intact chloroplast membranes. The data presented herein provide a simulation of the membrane appression phenomena using a single class of chloroplast-derived membrane subunits. The data demonstrate that specific surface-localized regions of the light-harvesting complex are involved in membrane-membrane interactions. 相似文献
47.
Measurements of proton translocation in CF1-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF0 is still dependent on light intensity with a first-order rate constant equal to mR0, where R0 is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF0 is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF1.CF0 complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities. 相似文献
48.
Electrophoretic light scattering (laser Doppler electrophoresis) has been employed to study the effects of guinea pig IgG
immune complexes on the electrophoretic mobility distributions of guinea pig resident peritoneal cells. The resident population
of cells is composed of macrophages (approximately 75%) and eosinophils (approximately 25%). These cells were separated according
to the well-established method of Boyum. Populations of resident macrophages, eosinophils, and the unfractionated samples
were incubated with soluble immune complexes, antigen alone, or antibody alone. The mean mobility of the resident macrophages
decreased approximately 60% when incubated in the presence of immune complexes, although no effect could be discerned in the
presence of antigen or antibody alone. The width of the resulting macrophage mobility distribution was larger than that of
the control distributions, with a broad shoulder on the high-mobility side, indicating a heterogeneous response of the macrophages
to the immune complexes. Eosinophils react in two distinct fashions. One population of eosinophils is present near the control
experiments. The second population reacts in a manner very similar to that of macrophages. This suggest that at least two
populations of eosinophils are present in the unstimulated guinea pig peritoneal cavity. Results that are intermediate between
these two cases are found when unfractionated samples are studied. 相似文献
49.
Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were incubated with trypsin or pronase for several hours. The indigestible residue was analyzed by polyacrylamide gel electrophoresis. Trypsinization resulted in a complete digestion of all proteins with the exception of the pigment-protein complexes as well as a polypeptide not yet characterized. Yet, as compared with untreated material, Complex II was found to have higher electrophoretic mobility. Electron-microscopic studies illustrate that the indigestible residue still has a preserved membrane structure. Disintegration of the thylakoid membranes by sodium dodecyl sulfate followed by trypsinization also resulted in the two complexes while all the other proteins were found to be digested. However, after removal of the lipids the protein moieties of the complexes proved to be easily digestible. From these results it is concluded that pigment-protein interaction may be an important factor in maintaining a conformation rather resistant to perturbants and proteases. In contrast to trypsin, pronase completely digested the polypeptides of the thylakoid membranes including the protein moieties of the pigment-protein complexes leaving an amorphous lipid mass. The results support the assumption that the complexes are necessary to maintain the membrane structure. 相似文献
50.
The NADP+ specific glutamate dehydrogenase from wild-type forms a stable binary complex with NADPH. This can combine with L-glutamate, α-ketoglutarate or the substrate analogue D-glutamate to form ternary complexes which can be distinguished by their different fluorescence properties. The affinity of the enzyme for NADPH diminishes with increases in pH or ionic strength of the solution. Experimental data obtained using modified glutamate dehydrogenases from mutant strains of suggest that the reduced-coenzyme binding sites observed fluorimetrically are the same as those observed by enzyme kinetics. 相似文献