全文获取类型
收费全文 | 472254篇 |
免费 | 49222篇 |
国内免费 | 176篇 |
出版年
2018年 | 4310篇 |
2016年 | 5662篇 |
2015年 | 6911篇 |
2014年 | 8525篇 |
2013年 | 12296篇 |
2012年 | 13676篇 |
2011年 | 14295篇 |
2010年 | 9784篇 |
2009年 | 8799篇 |
2008年 | 12684篇 |
2007年 | 13376篇 |
2006年 | 12529篇 |
2005年 | 11981篇 |
2004年 | 12176篇 |
2003年 | 11849篇 |
2002年 | 11690篇 |
2001年 | 21092篇 |
2000年 | 21363篇 |
1999年 | 16604篇 |
1998年 | 5523篇 |
1997年 | 5649篇 |
1996年 | 5262篇 |
1995年 | 5232篇 |
1994年 | 5128篇 |
1993年 | 5125篇 |
1992年 | 14179篇 |
1991年 | 13860篇 |
1990年 | 13495篇 |
1989年 | 13187篇 |
1988年 | 12341篇 |
1987年 | 11834篇 |
1986年 | 10686篇 |
1985年 | 10892篇 |
1984年 | 8954篇 |
1983年 | 7817篇 |
1982年 | 5852篇 |
1981年 | 5169篇 |
1980年 | 4998篇 |
1979年 | 8838篇 |
1978年 | 6791篇 |
1977年 | 6246篇 |
1976年 | 5756篇 |
1975年 | 6491篇 |
1974年 | 7186篇 |
1973年 | 7168篇 |
1972年 | 6634篇 |
1971年 | 6154篇 |
1970年 | 5296篇 |
1969年 | 5097篇 |
1968年 | 4655篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Modulation of K+ channels by hydrogen peroxide. 总被引:7,自引:0,他引:7
E Vega-Saenz de Miera B Rudy 《Biochemical and biophysical research communications》1992,186(3):1681-1687
External application of hydrogen peroxide (H2O2) was found to inhibit the time-dependent fast inactivation process of three cloned voltage-gated K+ channels expressed in Xenopus oocytes: KShIIIC, KShIIID and HukII. As expected from kinetic models where some channels are still opening while a significant fraction of channels is already inactivated there was a large increase in current magnitude concomitant to inactivation block. The channels otherwise functioned normally. The effects of H2O2 were specific (other cloned voltage-gated K+ channels were not affected), and reversible, the currents returned to normal upon removal of the H2O2. H2O2 is produced during normal metabolism; it could act as a modulator of excitability through effects on K+ channels if effective local concentrations are reached in neuronal regions close to the channel. KShIIIC and KShIIID currents are very similar to an O2-sensitive K+ current present in type I cells of the carotid body which is believed to underlie the modulation of excitability of these cells by changes in arterial O2 pressure. H2O2 has been proposed as an intermediary between O2 and cellular response in the carotid body; our results provide support for this model. 相似文献
52.
Possibilities of adventitious buds induction on the cotyledons obtained from sterile seedlings ofAbies concolor xAbies grandis hybrid were investigated. The following variables influencing bud induction and their further development were studied: the effect of expiant age, the effect of different growth regulators and their concentrations and duration of their application. The most suitable expiants proved to be the cotyledons of 7 d old seedlings. The most efficient cytokinin was benzylaminopurine (S mg l?1) in combination with napthaleneacetic acid (0.01 mg l?1). The most optimal duration of treatment was 17 to 21 d culture of explants on induction medium. Shoot growth was achieved on basal medium to which 14 mg 1?1 spermidine was added. 相似文献
53.
54.
The headshield of Monospilus dispar (Cladocera, Chydoridae, Aloninae) was characterized by the presence of a unique headpore. Scanning Electron Microscopy shows the occurrence of minute pores close to the main headpore. The intimate structure of the main headpore is formed by concentric lamellae. This new information leads to new considerations about phylogeny. 相似文献
55.
56.
F Jaisser C M Canessa J D Horisberger B C Rossier 《The Journal of biological chemistry》1992,267(24):16895-16903
In order to understand the molecular mechanism of ouabain resistance in the toad Bufo marinus, Na,K-ATPase alpha and beta subunits have been cloned and their functional properties tested in the Xenopus laevis oocyte expression system. According to sequence comparison between species, alpha 1, beta 1, and beta 3 isoforms were identified in a clonal toad urinary bladder cell line (TBM 18-23). The sequence of the alpha 1 isoform is characterized by two positively charged amino acids (Arg, Lys) at the N-terminal border of the H1-H2 extracellular loop and no charged amino acid at the C terminus, a pattern distinct from the ouabain-resistant rat alpha 1 isoform. The coexpression of alpha 1 beta 1 or alpha 1 beta 3 TBM subunits in the Xenopus oocyte resulted in the expression of identical maximum Na,K-pump currents with identical inhibition constant for ouabain (Ki) (alpha 1 beta 1: 53 +/- 3 microM; n = 7 vs. alpha 1 beta 3: 57 +/- 3.0 microM; n = 8) but distinct potassium half activation constant (K1/2) (alpha 1 beta 1: 0.87 +/- 0.08 mM, n = 16; alpha 1 beta 3: 1.29 +/- 0.07 mM, n = 17; p less than 0.005). We conclude that (i) the TBM alpha 1 isoform is necessary and sufficient to confer the ouabain resistant phenotype; (ii) the beta 3 or beta 1 subunit can associate with the alpha 1 equally well without affecting the ouabain-resistant phenotype; (iii) some specific sequence of the beta subunit can modulate the activation of the Na,K-pump by extracellular potassium ions. 相似文献
57.
58.
I Hübner I Steinmetz U Obst D Giebel D Bitter-Suermann 《Applied and environmental microbiology》1992,58(9):3187-3191
An immunological method for the detection of members of the family Enterobacteriaceae in drinking water was developed. The method was based on a sandwich enzyme-linked immunosorbent assay (ELISA) with monoclonal antibody immunoglobulin G2a 898 against enterobacterial common antigen. The enterobacterial common antigen sandwich ELISA combined with selective preenrichment culture could be performed in only 24 h. Six hundred sixty-eight water samples from a variety of German public water supplies were screened to verify the effectiveness of the new method. Ninety-eight percent of the results obtained by the immunological method could be confirmed by conventional microbiological methods. The immunological method proved to be considerably faster and more specific and sensitive than the standard method specified by the German drinking water regulations. 相似文献
59.
L N Kraeva V N Kokriakov V F Pozdnev V I Morozov A A Usova 《Biulleten' eksperimental'no? biologii i meditsiny》1992,113(6):600-601
Two fluorogenic derivatives of amino acids are proposed as substrates for the purpose of enzymatic assay: N-benzyloxycarbonyl-phenylalanine-4-methyl umbelliferyl ester (substrate-1) and tert-butyloxycarbonyl-alanine-4-methyl-umbelliferyl ester (substrate-II). Chymotrypsin-like (hydrolysis of substrate-1), elastase-like (hydrolysis of substrate-II) esterase activity of bovine pancreatic chymotrypsin, activities of cathepsin G and elastase from human, porcine and rat neutrophils and esterase activity of human, porcine and rat serum were assayed. Differences in the level of chymotrypsin-like and elastase-like activities of human, porcine and rat serum were established. Activities of purified elastase and cathepsin G from human and animal neutrophils were shown to have no significant distinctions. 相似文献
60.
S B Cheknev O L Latysheva L A Denisov F I Ershov 《Biulleten' eksperimental'no? biologii i meditsiny》1992,113(2):179-182
The cytotoxic activity of natural killer (NK) cells isolated from peripheral blood of 20 healthy donors and 34 patients with multiple sclerosis (MS) against labelled with H3-uridine target cells K-562 before and after their 1 hr treatment with reaferon (RF), T-activin (TA), myelopid (MP), opioid preparation dalargin (DL) as well as with combinations of TA, MP and DL with RF was studied in 14 hrs cytotoxic test. It has been shown that combination of RF with TA, MP and DL changed the regulatory action of these peptides on NK cell activity in healthy donors in vitro. The same combination of the preparations in patients with MS caused another changes in regulation of NK activity by them because NK cells in MS patients had had initially changed sensitivity to action of these regulatory polypeptides. 相似文献