全文获取类型
收费全文 | 12393篇 |
免费 | 1084篇 |
国内免费 | 3篇 |
专业分类
13480篇 |
出版年
2023年 | 43篇 |
2022年 | 128篇 |
2021年 | 253篇 |
2020年 | 147篇 |
2019年 | 169篇 |
2018年 | 231篇 |
2017年 | 182篇 |
2016年 | 317篇 |
2015年 | 577篇 |
2014年 | 568篇 |
2013年 | 729篇 |
2012年 | 992篇 |
2011年 | 1038篇 |
2010年 | 633篇 |
2009年 | 539篇 |
2008年 | 860篇 |
2007年 | 860篇 |
2006年 | 769篇 |
2005年 | 718篇 |
2004年 | 764篇 |
2003年 | 632篇 |
2002年 | 647篇 |
2001年 | 109篇 |
2000年 | 68篇 |
1999年 | 106篇 |
1998年 | 164篇 |
1997年 | 115篇 |
1996年 | 110篇 |
1995年 | 97篇 |
1994年 | 84篇 |
1993年 | 76篇 |
1992年 | 57篇 |
1991年 | 65篇 |
1990年 | 42篇 |
1989年 | 41篇 |
1988年 | 43篇 |
1987年 | 39篇 |
1986年 | 52篇 |
1985年 | 42篇 |
1984年 | 44篇 |
1983年 | 45篇 |
1982年 | 40篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 25篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 24篇 |
1974年 | 16篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The ability of aras protein to associate with proteins present in rat brain cytosolin vitro was investigated using chemical cross-linking agents and the125I-labelled v-H-ras protein. Two iodinated protein complexes with apparent molecular weights of 40 and 85 kDa were observed when a mixture of rat brain cytosol and [125I]ras was treated with the cross-linking agent disuccinimidyl suberate and subjected to SDS-PAGE. Formation of the [125I] 85 kDa complex was enhanced by a high concentration of EDTA while generation of the 40 kDa species was abolished by this treatment. Formation of the [125I] 85 kDa complex was inhibited by unlabelledras protein, GTP, GTPS, and GDP but not by ATPS and GMP.Chromatography of the cross-linked brain cytosol-[125I]ras mixture on DEAE cellulose partially resolved the [125I] 85 kDa complex from the [125I]ras protein. The [125I] 85 kDa complex (formed using ethyleneglycolbis (succinimidylsuccinate) as the cross-linking agent) could be immunoprecipitated using a rabbit anti-ras polyclonal antibody. Treatment of the immunoprecipitate with hydroxylamine to cleave the cross-link yielded [125I]-labelledras. A substantial enrichment of the proportion of the [125I] 85 kDa complex in the cross-linked extract was achieved by preparative SDS-PAGE. It is concluded that thein vitro chemical cross-linking approach employed here has detected tworas binding proteins in rat brain cytosol: a 65 kDa heat-sensitive and a 20 kDa heat-stable protein. The possibility that the 65 kDaras binding protein is aras regulatory orras effector protein which has not so far been characterised is briefly discussed.Abbreviations DSS
disuccinimidyl suberate
- EGS
ethyleneglycolbis (succinimidylsuccinate)
- GTPS
guanosine 5-[-thio] triphosphate
- ATPS
adenosine 5-[-thio] triphosphate 相似文献
92.
Timothy P. L. Smith Nestor Lopez-Corrales Michael D. Grosz Craig W. Beattie Steven M. Kappes 《Mammalian genome》1997,8(5):333-336
We report the placement of 34 new microsatellite (ms) markers, isolated from a lambda phage genomic clone library, on the
bovine genetic map by linkage to published markers. Five of these markers lie at or near the ends of linkage groups and are
used to establish chromosomal coverage and orientation. Fluorescence in situ hybridization (FISH) analysis demonstrates that
the linkage groups on the U.S. Meat Animal Research Center (MARC) map extend to the telomeric region of Chromosomes (Chrs)
7 and 10. Linkage groups on Chrs 4, 6, and 14 appear to be less inclusive.
Received: 23 September 1996 / Accepted: 28 December 1996 相似文献
93.
Mary C. O'Sullivan Qibing Zhou Zhili Li Timothy B. Durham Donna Rattendi Schennella Lane Cyrus J. Bacchi 《Bioorganic & medicinal chemistry》1997,5(12):2145-2155
Trypanothione reductase (TR) occurs exclusively in trypanosomes and leishmania, which are the etiological agents of many diseases. TR plays a vital role in the antioxidant defenses of these parasites and inhibitors of TR have potential as antitrypanosomal agents. We describe the syntheses of several spermine and spermidine derivatives and the inhibiting effects of these compounds on T. cruzi TR. All of the inhibiting compounds displayed competitive inhibition of TR-mediated reduction of trypanothione disulfide. The three most effective compounds studied were N4,N8-bis(3-phenylpropyl)spermine (12), N4,N8-bis(2-naphthylmethyl)spermine (14), and N1,N8-bis(2-naphthylmethyl)spermidine (21), with Ki values of 3.5, 5.5 and 9.5 μM, respectively. Compounds 12, 14, and 21 were found to be potent trypanocides in vitro with IC50 values ranging from 0.19 to 0.83 μM against four T. brucei ssp. strains. However, these compounds did not prolong the lives of mice infected with trypanosomes. This work indicates that certain polyamine derivatives which target a unique pathway in Trypanosomatidae have potential as antitrypanosomal agents. 相似文献
94.
Yarus Sinai Greenberg Norman M. Wei Yongli Whitsett Jeffrey A. Weaver Timothy E. Rosen Jeffrey M. 《Transgenic research》1997,6(1):51-57
Because of the apparent clinical importance of human pulmonary surfactant B (SP-B), the expression of SP-B was directed to the mammary gland of transgenic mice using previously characterized rat whey acidic protein (WAP) regulatory sequences. rWAP/SP-B mRNA was expressed specifically in the mammary gland, and ranged from 1 to 5% of the endogenous WAP mRNA levels. SP-B was detected immunologically in both tissue and milk. The transgene product had an apparent molecular weight of 40--45 kDa, corresponding to the predicted size of the SP-B proprotein. Incubation of an SP-B-enriched fraction of milk with cathepsin D in vitro produced 20--25 kDa species, consistent with cleavage of the amino terminal domain by cathepsin D. This was confirmed using antibodies specific to the carboxy-terminal domain of SP-B. However, the appearance of only the SP-B proprotein in milk suggests that cathepsin D is not involved in the in vivo processing of SP-B. The SP-B proprotein can be expressed in milk of transgenic mice without any observed effects on mammary gland morphology or lactation 相似文献
95.
Timothy S. McClintock Fuqiang Xu Jorge Quintero Anne M. Gress Teresa M. Landers 《Journal of neurochemistry》1997,68(6):2248-2254
Abstract: We have isolated from an American lobster ( Homarus americanus ) olfactory organ cDNA library a clone, hGαq , with >80% identity to mammalian and arthropod Gαq sequences. In brain and olfactory organ, hGαq mRNA was expressed predominantly in neurons, including virtually all the neuronal cell body clusters of the brain. Gαq protein was also expressed broadly, appearing on western blots as a single band of 46 kDa in brain, eyestalk, pereiopod, dactyl, tail muscle, olfactory organ, and aesthetasc hairs. These results suggest that hGαq plays a role in a wide variety of signal transduction events. Its presence in the olfactory aesthetasc hairs, which are almost pure preparations of the outer dendrites of the olfactory receptor neurons, the expression of a single hGαq mRNA species (6 kb) in the olfactory organ, and the localization of hGαq mRNA predominantly in the olfactory receptor neurons of the olfactory organ strongly suggest that one function of hGαq is to mediate olfactory transduction. 相似文献
96.
97.
Michael Hoppert Timothy J. Mahony Frank Mayer David J. Miller 《Archives of microbiology》1995,163(4):300-306
The hydroxylamine oxidoreductase from Nitrosomonas europaea was prepared to apparent electrophoretic homogeneity. Electron microscopy of negatively stained preparations of the sample revealed an overall diameter of about 8.8 nm of the enzyme particle. The native structure was determined as a tetrahedron-like assembly of identical subunits exhibiting four protein masses.Abbreviations
ESI
Electron spectroscopic imaging
-
HAO
Hydroxylamine oxidoreductase 相似文献
98.
Five models have been built by the ICM method for the Comparative Modeling section of the Meeting on the Critical Assessment of Techniques for Protein Structure Prediction. The targets have homologous proteins with known three-dimensional structure with sequence identity ranging from 25 to 77%. After alignment of the target sequence with the related three-dimensional structure, the modeling procedure consists of two subproblems: side-chain prediction and loop prediction. The ICM method approaches these problems with the following steps: (1) a starting model is created based on the homologous structure with the conserved portion fixed and the noncon-served portion having standard covalent geometry and free torsion angles; (2) the Biased Probability Monte Carlo (BPMC) procedure is applied to search the subspaces of either all the nonconservative side-chain torsion angles or torsion angles in a loop backbone and surrounding side chains. A special algorithm was designed to generate low-energy loop deformations. The BPMC procedure globally optimizes the energy function consisting of ECEPP/3 and solvation energy terms. Comparison of the predictions with the NMR or crystallographic solutions reveals a high proportion of correctly predicted side chains. The loops were not correctly predicted because imprinted distortions of the backbone increased the energy of the near-native conformation and thus made the solution unrecognizable. Interestingly, the energy terms were found to be reliable and the sampling of conformational space sufficient. The implications of this finding for the strategies of future comparative modeling are discussed. © 1995 Wiley-Liss, Inc. 相似文献
99.
A discrete, environmentally coupled, size-specific model of microbial population dynamics in continuous culture is presented. It is mathematically simpler than other models based on similar assumptions and lends itself to numerical and analytic solutions. It displays several phenomena which have been reported in the experimental literature but which are not well understood; specifically, a loose relationship between biomass and numbers (i.e., a time lag between mass growth and cell division) and a critical damping of biomass while numbers continue to oscillate. In addition, the model provides several new predictions: The stable biomass distribution is independent of the environmental factors considered in the model and uniformly distributes the biomass among the size classes. The rate of approach to stability and the frequency of waves through the size distributions are a function of the flow rate and the variance in rate of growth and size at division. The model should provide a useful basis for studying the effects of size specificity on the dynamics of microbial populations cultured in chemostats. 相似文献
100.
We have used the enzyme elastase to remove the basal lamina of epithelia from two insects: the upper Malpighian tubules of Rhodnius prolixus and imaginai discs of Drosophila melanogaster. Removal of the basal lamina was confirmed using scanning and transmission electron microscopy. Use of the technique on the Malphighian tubules of Rhodnius reveals for the first time the three-dimensional organization of the circumferential folds of the basal plasma membrane. Elastase is much more effective in removing the basal lamina than are the enzymes hyaluronidase, collagenase, and chymotrypsin, either alone or in combination. Following elastase treatment, cells of the Malpighian tubules dissociate with only mild mechanical agitation into single, viable cells. Treatment with elastase removes the basal laminae of imaginai discs of Drosophila and accelerates evagination as has been previously described for trypsin. To obtain single cell preparations from elastase-treated imaginai discs, mechanical stirring in Ringer low in Ca2+ was required. In addition to its usefulness in cell isolation, elastase treatment allows examination of the effect of removal of basal laminae on the physiology and development of insect epithelia. 相似文献