全文获取类型
收费全文 | 15657篇 |
免费 | 1051篇 |
国内免费 | 7篇 |
出版年
2024年 | 17篇 |
2023年 | 49篇 |
2022年 | 109篇 |
2021年 | 309篇 |
2020年 | 204篇 |
2019年 | 284篇 |
2018年 | 407篇 |
2017年 | 348篇 |
2016年 | 572篇 |
2015年 | 862篇 |
2014年 | 986篇 |
2013年 | 1064篇 |
2012年 | 1440篇 |
2011年 | 1332篇 |
2010年 | 877篇 |
2009年 | 680篇 |
2008年 | 1007篇 |
2007年 | 891篇 |
2006年 | 814篇 |
2005年 | 747篇 |
2004年 | 731篇 |
2003年 | 576篇 |
2002年 | 475篇 |
2001年 | 380篇 |
2000年 | 351篇 |
1999年 | 245篇 |
1998年 | 109篇 |
1997年 | 91篇 |
1996年 | 63篇 |
1995年 | 63篇 |
1994年 | 50篇 |
1993年 | 42篇 |
1992年 | 88篇 |
1991年 | 63篇 |
1990年 | 45篇 |
1989年 | 52篇 |
1988年 | 29篇 |
1987年 | 34篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1970年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
81.
Summary Double fluorescent labeling, with fluorescein isothiocyanate (FITC)-labeled F(ab)2 specific for the heavy chain and R-phycoerythrin (R-PE)-labeled F(ab)2 specific for the light chain, was demonstrated as a convenient means for the accurate evaluation of a heterogeneous non-antibody-producing population. Furthermore, it could be used for monitoring the changes in each immunoglobulin (Ig) chain content of the cells during the batch culture, which will facilitate the study on antibody synthesis, assembly and secretion. 相似文献
82.
Summary In the production of L-cysteine from D,L-ATC stability of the relevant enzymes produced byPseudomonas sp. was tested, and strategies to improve the stability of L-ATC hydrolase were investigated in view of water activity and ionic strength. Among the three enzymes which participate in L-cysteine production, i.e., ATC racemase, L-ATC hydrolase, and S-carbamyl-L-cysteine hydrolase, L-ATC hydrolase is the least stable. Various mixtures of salts and sorbitol were added to adjust the water activities of the tested solutions. As water activity decreased from 0.93 to 0.80, the stability of L-ATC hydrolase was sharply enhanced. In the absence of sorbitol the stability of L-ATC hydrolase increased in proportion to ionic strength. Even though enzyme stability was not good at a low ionic strength, it was enhanced by lowering water activity with addition of sorbitol. The half life of L-ATC hydrolase in sorbitol-salt mixtures increased by tenfold to twentyfold compared to that of a control. 相似文献
83.
Summary Xanthate floatation compounds, added to cultures of Thiobacillus ferrooxidans leaching chalcopyrite, inhibited growth in the concentration range 1–10 mM and caused a drop in formation of soluble copper and iron. Maximum (80–90%) growth inhibition was at 10 mM for isobutyl-, amyl- and ethyl xanthate while isopropyl xanthate was innocuous but caused a four-fold increase in lag phase. Copper production was depressed by 30% for isopropyl-, 53% for isobutyl-, ethyl- and 77% for amyl xanthate at 10 mM additions. 相似文献
84.
Mixed-phase plants of Griffithsia japonica Okamura spontaneously occurred in a laboratory culture. Four female plants produced tetrasporangia and spermatangia in addition to their normal female reproductive structures (bisexual/mixed-phase plants), and four male plants produced tetrasporangia as well as spermatangia (male/mixed-phase plants). To determine the nuclear ploidy level of these mixed-phase plants, relative nuclear sizes of male, female, tetrasporangial, and mixed-phase plants were measured using a microscopic image analysis system. Haploid gametophytes could be distinguished from diploid tetrasporophytes by relative nuclear sizes, with the later having nuclei twice the size of the former. Relative nuclear sizes of the mixed-phase plants were similar to those of the haploid plants. Thus, the mixed-phase plants were determined to be haploid. Haploid mixed-phase plants of G. japonica have a potential to produce male, female and tetrasporangial reproductive structures. Sex determination models are discussed to explain "haploid" mixed-phase phenomena in red algae . 相似文献
85.
Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd- (FG, Cucurbita ficifolia Bouché)seedlings in order to determine the effect of solution temperature(12, 22, and 32°C) on the mineral composition of xylem sapand the plasma membrane K+-Mg++-ATPase activities of the roots.Low solution temperature (12°C) lowered the concentrationof NO3 and H2PO4 in xylem sap of CG plants butnot of FG plants. Concentrations of K+, Ca++ and Mg++ in xylemsap were less affected than anions by solution temperature.The plasma membrane of FG plants grown in 12°C solutiontemperature showed the highest K+- Mg++-ATPase activity at allATP concentrations up to 3 mM and at low reaction temperatureup to 12°C, indicating resistance of figleaf gourd to lowroot temperature. (Received December 27, 1994; Accepted March 10, 1995) 相似文献
86.
Hyung-Joo Jin Jeong–Ha Kim Chul Hyun Sohn R.E. DeWreede Tae–Joo Choi G.H.N. Towers J.B. Hudson Yong–Ki Hong 《Journal of applied phycology》1997,9(4):383-388
Fifty-nine species of marine macrophytes from the coasts of British Columbia, Canada and Korea have been screened for the
presence of PCR inhibitors, namely inhibitors of Taq DNA polymerase. Eleven of the species displayed some inhibitor activity.
At the concentration of 5 μg of methanol extract in 25μL reaction mixture of PCR containing 1.5 unit of Taq DNA polymerase,
one (Ulva sp.) of 8 Chlorophyta, eight (Colpomenia bullosa, Ecklonia cava, Endarachne binghamiae, Fucus distichus, Hizikia
fusiformis, Sargassum confusum, Sargassum sagamianum, and Sargassum thunbergii) of 28 Phaeophyta, and one (Symphyocladia latiuscula)
of 34 Rhodophyta showed inhibition in PCR amplification. In the case of the water extract, two (Cladophora columbiana, Ulva
sp.) Chlorophyta, seven (Endarachne binghamiae, Fucus distichus, Hizikia fusiformis, Sargassum confusum, Sargassum sagamianum,
Sargassum horneri, Scytosiphon dotyi) Phaeophyta, no Rhodophyta and one (Phyllospadix scouleri) seagrass showed inhibition
in PCR amplification. the methanol fraction of Sargassum confusum and the water fraction of Fucus gardneri (mid–intertidal)
have been found to inhibit PCR at level as low as 0.5 μg in 25μL of PCR reaction mixture.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
87.
To understand the role of chromatin structure in the expression of the mouse protamine 1, protamine 2, and transition protein
2 genes during spermatogenesis, we have examined the genomic organization of this cluster of ``haploid-specific' genes. As
seen in the human genome, protamine 2, transition protein 2, and approximately 2.8 kb of a CpG island, hereafter called CpG
island-dTP2, were clustered in a small region. Methylation analyses of this region have demonstrated that i) unlike most other
tissue-specific genes, the protamine 1, protamine 2, and transition protein 2 genes were located in a large methylated domain
in round spermatids, the cell type where they are transcribed, ii) the protamine 1 gene was only partially methylated in somatic
cells and in testes from 7-day-old mice, and iii) the approximately 2 kb upstream and downstream of the CpG island-dTP2 were
only partially methylated in somatic tissues. DNase I analysis revealed the presence of at least five strong DNase I hypersensitive
sites over the CpG island-dTP2 in somatic tissues, but not in germ cells, and sequence analysis indicated that the CpG island-dTP2
is homologous to a CpG island located approximately 10.6 kb downstream of the human transition protein 2 gene. Although the
nature of a CpG island-dTP2 and the function of a CpG island-dTP2-containing somatic tissue-specific DNase I hypersensitive
sites in close proximity to the germ cell-specific gene cluster are unclear, the ``open' chromatin structure of the CpG island-dTP2
may be responsible for the partial methylation pattern of the flanking sequences including the transition protein 2 gene in
somatic tissues.
Received: 6 September 1996 / Accepted: 14 January 1997 相似文献
88.
T. N. Ferraro G. T. Golden G. G. Smith N. J. Schork P. St. Jean C. Ballas H. Choi W. H. Berrettini 《Mammalian genome》1997,8(3):200-208
Mature DBA/2J (D2) mice are very sensitive to seizures induced by various chemical and physical stimuli, whereas C57BL/6J
(B6) mice are relatively seizure resistant. We have conducted a genome-wide search for quantitative trait loci (QTLs) influencing
the differential sensitivity of these strains to kainic acid (KA)-induced seizures by studying an F2 intercross population. Parental, F1, and F2 mice (8–10 weeks of age) were injected subcutaneously with 25 mg/kg of KA and observed for 3 h. Latencies to focal and generalized
seizures and status epilepticus were recorded and used to calculate an overall seizure score. Results of seizure testing indicated
that the difference in susceptibility to KA-induced seizures between D2 and B6 mice is a polygenic phenomenon with at least
65% of the variance due to genetic factors. First-pass genome screening (10-cM marker intervals) in F2 progeny (n = 257) documented a QTL of moderate effect on Chromosome (Chr) 1 with a peak LOD score of 5.5 (17% of genetic
variance explained) localized between D1Mit30 and D1Mit16. Provisional QTLs of small effect were detected on Chr 11 (D11Mit224–D11Mit14), 15 (D15Mit6–D15Mit46) and 18 (D18Mit9–D18Mit144). Multiple locus models generally confirmed the Mapmaker/QTL results and also provided evidence for another QTL on Chr 4
(D4Mit9). Multilocus analysis of seizure severity suggested that additional loci on Chrs 5 (D5Mit11), 7 (D7Mit66), and 15 (D15Nds2) might also contribute to KA-induced seizure response. Overall, our results document a complex genetic determinism for KA-induced
seizures in these mouse strains with contributions from as many as eight QTLs.
Received: 16 April 1996 / Accepted: 21 October 1996 相似文献
89.
90.
Seung B. Ha Neli Melman Kenneth A. Jacobson Vasu Nair 《Bioorganic & medicinal chemistry letters》1997,7(24):1698-3090
N6-Substituted adenosine analogues containing cyclic hydrazines or chiral hydroxy (ar)alkyl groups, designed to interact with the S2 and S3 receptor subregions, have been synthesized and their binding to the adenosine A1 and A2A receptors have been investigated. Examples of both types of compounds were found to exhibit highly selective binding (Ki in low nM range) to the rat A1 receptor. 相似文献