全文获取类型
收费全文 | 6564篇 |
免费 | 619篇 |
国内免费 | 322篇 |
出版年
2024年 | 13篇 |
2023年 | 79篇 |
2022年 | 175篇 |
2021年 | 305篇 |
2020年 | 180篇 |
2019年 | 197篇 |
2018年 | 192篇 |
2017年 | 137篇 |
2016年 | 214篇 |
2015年 | 414篇 |
2014年 | 426篇 |
2013年 | 493篇 |
2012年 | 570篇 |
2011年 | 524篇 |
2010年 | 279篇 |
2009年 | 245篇 |
2008年 | 350篇 |
2007年 | 287篇 |
2006年 | 265篇 |
2005年 | 259篇 |
2004年 | 226篇 |
2003年 | 195篇 |
2002年 | 174篇 |
2001年 | 107篇 |
2000年 | 124篇 |
1999年 | 117篇 |
1998年 | 70篇 |
1997年 | 53篇 |
1996年 | 38篇 |
1995年 | 37篇 |
1994年 | 44篇 |
1993年 | 43篇 |
1992年 | 71篇 |
1991年 | 57篇 |
1990年 | 46篇 |
1989年 | 56篇 |
1988年 | 50篇 |
1987年 | 35篇 |
1986年 | 41篇 |
1985年 | 33篇 |
1984年 | 50篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1975年 | 16篇 |
1971年 | 11篇 |
排序方式: 共有7505条查询结果,搜索用时 390 毫秒
101.
102.
An analysis of the unconfined compression of articular cartilage 总被引:7,自引:0,他引:7
Analytical solutions have been obtained for the internal deformation and fluid-flow fields and the externally observable creep, stress relaxation, and constant strain-rate behaviors which occur during the unconfined compression of a cylindrical specimen of a fluid-filled, porous, elastic solid, such as articular cartilage, between smooth, impermeable plates. Instantaneously, the "biphasic" continuum deforms without change in volume and behaves like an incompressible elastic solid of the same shear modulus. Radial fluid flow then allows the internal fluid pressure to equilibrate with the external environment. The equilibrium response is controlled by the Young's modulus and Poisson's ratio of the solid matrix. 相似文献
103.
A Marongiu P Nuvole P Lai F Sau G Bomboi P Bini 《Bollettino della Società italiana di biologia sperimentale》1984,60(2):307-311
It has been studied the total plasma cholesterol rate in lactating or dry sheep and goats of Sardinian breed. The values obtained for the four different groups of subjects have been compared with the "t of Student". While the difference between the sheep groups has seemed very accentuated, it has appeared hardly significant between the goat groups. Highly significant difference has also been found between lactating sheep and goats whereas there was no significant difference among the groups of dry subjects. 相似文献
104.
Using the spin trap, 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) we have demonstrated that hydroxyl radicals are generated indirectly from purified preparations of rat liver microsomal NADPH-cytochrome c (P-450) reductase during NADPH oxidation. Hydroxyl radical formation is completely inhibited by p-chloromercuribenzoate, but not by metyrapone. In addition, hydroxyl radical DMPO adduct formation is blocked by added linolenic acid which, in turn, is peroxidatively degraded into malondialdehyde, suggesting that hydroxyl radicals formed from purified NADPH-cytochrome c (P-450) reductase are capable of initiating lipid peroxidation. A mechanism for the indirect production of hydroxyl radicals from NADPH-cytochrome P-450 reductase is discussed. 相似文献
105.
Electron microscope study of the base sequence homology between simian virus 40 and human papovavirus BK. 下载免费PDF全文
The base sequence homology between the genomes of simian virus 40 (SV40) and human papovavirus BK (BKV) was studied by the heteroduplex method of Ferguson and Davis (J. Mol. Biol. 94:135-149, 1975). When mounted for microscopy in 30% formamide (Tm-35 degrees C), BKV/SV40 heteroduplexes were an average of 92% double-stranded and contained only two small nonhomologous regions that mapped near the junctions between the early and late regions of the SV40 Genome. At higher formamide concentrations, the fraction of duplex DNA in the BKV/SV40 heteroduplexes decreased, indicating significant base mismatching in the homologous regions. The strongest regions of homology were located in the late region. 相似文献
106.
We report here the complete synthesis of the spin-labeled derivative of an antitumor ether phospholipid, 1-O-octadecyl-2-O-(4'-doxylpentyl)-rac-glycerol-3-phosphocholine. This also represents the first time that the synthesis of a nitroxide spin-labeled diether phospholipid is described. In vitro experiments showed that at micromolar concentrations, this new analog is readily incorporated into the plasma membranes of human HL60 and mouse E8/AK.D1 leukemic cells, and subsequently kills the cells. The availability of this new probe should permit the electron spin resonance spectroscopic approach to investigate ways by which anti-tumor ether phospholipids selectively destroy the tumor cells. 相似文献
107.
A computer-assisted comparative analysis of the amino acid sequences of (putative) thiol proteases encoded by the genomes of several diverse groups of positive-stranded RNA viruses and distantly related to the family of cellular papain-like proteases is presented. A high level of similarity was detected between the leader protease of foot-and-mouth-disease virus and the protease of murine hepatitis coronavirus which cleaves the N-terminal p28 protein from the polyprotein. Statistically significant alignment of a portion of the rubella virus polyprotein with cellular papain-like proteases was obtained, leading to tentative identification of the papain-like protease as the enzyme mediating processing of the non-structural proteins of this virus. Specific grouping between the sequences of the proteases of alpha-viruses, and poty- and bymoviruses was revealed. It was noted that papain-like proteases of positive-stranded RNA viruses are much more variable both in their sequences and in genomic locations than chymotrypsin-related proteases found in the same virus class. A novel conserved domain of unknown function has also been identified which flanks the papain-like proteases of alpha-, rubi- and coronaviruses. 相似文献
108.
Distribution of compatible solutes in the halophilic methanogenic archaebacteria. 总被引:18,自引:6,他引:12 下载免费PDF全文
M C Lai K R Sowers D E Robertson M F Roberts R P Gunsalus 《Journal of bacteriology》1991,173(17):5352-5358
Accumulation of compatible solutes, by uptake or de novo synthesis, enables bacteria to reduce the difference between osmotic potentials of the cell cytoplasm and the extracellular environment. To examine this process in the halophilic and halotolerant methanogenic archaebacteria, 14 strains were tested for the accumulation of compatible solutes in response to growth in various extracellular concentrations of NaCl. In external NaCl concentrations of 0.7 to 3.4 M, the halophilic methanogens accumulated K+ ion and low-molecular-weight organic compounds. beta-Glutamate was detected in two halotolerant strains that grew below 1.5 M NaCl. Two unusual beta-amino acids, N epsilon-acetyl-beta-lysine and beta-glutamine (3-aminoglutaramic acid), as well as L-alpha-glutamate were compatible solutes among all of these strains. De novo synthesis of glycine betaine was also detected in several strains of moderately and extremely halophilic methanogens. The zwitterionic compounds (beta-glutamine, N epsilon-acetyl-beta-lysine, and glycine betaine) and potassium were the predominant compatible solutes among the moderately and extremely halophilic methanogens. This is the first report of beta-glutamine as a compatible solute and de novo biosynthesis of glycine betaine in the methanogenic archaebacteria. 相似文献
109.
“雄茭”、灰茭形成规律的初步研究 总被引:6,自引:2,他引:4
茭白栽培过程中,常会出现“雄茭”和灰茭分蘖。根据对茭白的形态学观察,认识到:“雄茭”分蘖的产生是分蘖期母茎中茭白黑粉菌菌丝未能入侵新生分蘖腋芽而导致的结果;灰茭分蘖是因其菌丝的潜育期比正常茭短,故在苗端的膨大部分较早地产生了不同程度的黑粉孢子堆。 相似文献
110.