全文获取类型
收费全文 | 407630篇 |
免费 | 34822篇 |
国内免费 | 965篇 |
专业分类
443417篇 |
出版年
2018年 | 15968篇 |
2017年 | 14937篇 |
2016年 | 11772篇 |
2015年 | 4736篇 |
2014年 | 5224篇 |
2013年 | 7058篇 |
2012年 | 12846篇 |
2011年 | 23179篇 |
2010年 | 19457篇 |
2009年 | 15488篇 |
2008年 | 19064篇 |
2007年 | 21446篇 |
2006年 | 7517篇 |
2005年 | 8372篇 |
2004年 | 8112篇 |
2003年 | 8159篇 |
2002年 | 7704篇 |
2001年 | 17561篇 |
2000年 | 17716篇 |
1999年 | 13324篇 |
1998年 | 3877篇 |
1997年 | 4151篇 |
1996年 | 3875篇 |
1995年 | 3491篇 |
1994年 | 3474篇 |
1993年 | 3576篇 |
1992年 | 10415篇 |
1991年 | 10372篇 |
1990年 | 9814篇 |
1989年 | 9653篇 |
1988年 | 9007篇 |
1987年 | 8378篇 |
1986年 | 7561篇 |
1985年 | 7408篇 |
1984年 | 5837篇 |
1983年 | 5099篇 |
1982年 | 3629篇 |
1981年 | 3184篇 |
1980年 | 3035篇 |
1979年 | 5351篇 |
1978年 | 4116篇 |
1977年 | 3752篇 |
1976年 | 3300篇 |
1975年 | 3788篇 |
1974年 | 3947篇 |
1973年 | 3891篇 |
1972年 | 4078篇 |
1971年 | 3816篇 |
1970年 | 2829篇 |
1969年 | 2741篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
T Henry A Ferguson 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(2):491-496
Informative crosses have verified the genetic basis of a polymorphism at the Ldh-1 locus in brown trout and enzyme activity measurements indicate that the previously described polymorphism at this locus is best explained by a null allele. The LDH-1, LDH-2, LDH-3 and LDH-4 homotetrameric isozymes were purified and subjected to enzyme kinetic analysis. While LDH-1 and LDH-2 displayed catalytic equivalence, important kinetic differences were found between the LDH-3 and LDH-4 isozymes. 相似文献
992.
Analgesic effects of dynorphin-A and morphine in mice 总被引:3,自引:0,他引:3
To investigate whether or not dynorphin-A is analgesic, the effect of this peptide was tested in comparison with that of morphine in mice. Dynorphin-A produced a potent analgesic effect in the acetic acid writhing and tail pinch tests, but a weak effect in the tail flick test when given by intracerebroventricular injection. In contrast, morphine caused a potent analgesia in all the tests. Dynorphin-A was more effective when given by intrathecal injection than by intracerebroventricular injection, whereas morphine was equipotent by both injection routes. The results suggest that dynorphin-A is analgesic and that its analgesia may be differentiated from that of morphine. 相似文献
993.
The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by
heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model
known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition,
are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the
X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy
yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and
(C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial
confinement fusion experiments with the use of laser radiation and heavy-ion beams. 相似文献
994.
The use of a mixture model in the analysis of count data 总被引:1,自引:0,他引:1
A mixture model is presented for the analysis of data on premature ventricular contractions. The analysis is shown to be straightforward and the conclusions relatively simple. 相似文献
995.
The subtypes of meningococci are defined by antigenic determinants on the class 1 outer membrane proteins. The established subtypes, designated by P1 and a number according to the prototype reference strain on which they were first recognized by monoclonal antibodies, includes P1.2, P1.9, P1.15 and P1.16. We have investigated more prototype reference strains, using new monoclonal antibodies, and identified the new subtypes P1.1, P1.6 and P1.1,16. The P1.1,16 epitope is found on both the P1.1 and the P1.16 reference strains, but not on all P1.1 and P1.16 strains and can occur independently from the P1.1 and the P1.16 epitopes. It appears that class 1 outer membrane proteins contain at least two independent subtype-specific epitopes. For clarity, we now redefine P1.1,16 as P1.7, permitting thus the identification of strains of P1.1, P1.1,7, P1.7, P1.7,16 and P1.16 subtypes. It can clearly be expected that more class 1 outer membrane protein determinants will be recognized as more monoclonal typing antibodies are produced. The monoclonal antibodies now available to us can subtype 80-90% of group B and C meningococci; they also react with group A meningococci, but not with other Neisseriae. The immunological dissection of these subtyping antigens will improve our understanding of the relationship between components of the bacteria and the induction or prevention of disease. 相似文献
996.
Structural analysis of human profilin has revealed two tryptophan residues, W3 and W31, which interact with polyproline. The codons for these residues were mutated to encode phenylalanine and the mutant proteins overexpressed in Eschericia coli. The isolated proteins were diminished in their ability to bind polyproline, whereas phosphatidylinositol 4,5-bisphosphate (PIP2) binding remained unchanged. In many strains of Saccharomyces cerevisiae, disruption of the gene encoding profilin, PFY1, is lethal. It was found that expression of the gene for human profilin is capable of suppressing this lethality. The polyproline-binding mutant alleles of the human gene were cloned into various yeast expression vectors. Each of the mutant genes resulted in suppression of the lethality of pfy1Delta. It was observed that the mutant protein expression levels paralleled the growth rates of the strains. The severity of various morphological abnormalities of the strains was also attenuated with increased protein levels, suggesting that profilin polyproline-binding mutations are deleterious to cell growth unless overexpressed. Both tryptophan mutations were combined to give a third mutant allele that was found both unable to bind polyproline and to suppress the lethality of a pfy1 deletion. Immunoprecipitation experiments suggested that the mutants were unaltered in their affinity for actin and PIP2. These data strongly suggest that polyproline binding is an essential function of profilin. 相似文献
997.
Uncharged poly(Nε-methyl-L -lysine) (PMLL) and its isomer, poly(Nδ-ethyl-L -ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix-to-β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L -lysine) (PLL). The rate of conversion follows the order: PMLL < PELO < PLL. The helix can be regenerated upon cooling near zero degrees, for instance, after more than 12 hr at 2°C. At concentrations less than 0.02% the β form is intramolecular, but at higher concentrations both intra- and intermolecular β forms are generated. Poly(Nδ-methyl-L -ornithine) (PMLO), an isomer of PLL, behaves like poly(L -ornithine); uncharged PMLO in alkaline solution is partially helical and becomes disordered at elevated temperatures. 相似文献
998.
An electron histochemical study was undertaken to localize calcium with ammonium oxalate precipitation technique in soleus muscle of rat in normal cases and in myopathy induced experimentally by a prolonged treatment of 2,4-dichlorophenoxyacetate (2,4-D). The calcium content of precipitates was detected by energy-dispersive X-ray microanalysis. In normal cases, the electron dense precipitates containing calcium were mainly found in the vesicles of sarcoplasmic reticulum, whereas in 2,4-D induced myopathy the deposits were shifted near the Z line into the myofibrils. Calcium, because the uptake into sarcoplasmic vesicles was inhibited by 2,4-D, could attach to other binding sites, such as to the troponin-C.A long-lasting binding of calcium might lead to a prolonged activation of the actin-myosin system. 相似文献
999.
T S Minina E A Andreevskaia I V Domaradski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1978,(10):61-66
Use of E. coli strains with phenotypes Rec+ and Rec- asrecipients in intergenera crosses confirmed the supposition put forward by the authors formerly that new chromosomal markers in transconjugantes originated due to Psuedomonas aeruginosa. These chromosomal markers were transferred together with plasmid R conditioning the conjugation, and maintained without being built-into E. coli chromosome. Between the arg+ marker and the plasmid R18 there existed labile physical connection demonstrable only under definite conditions of recombinant selection. 相似文献
1000.