全文获取类型
收费全文 | 62185篇 |
免费 | 5275篇 |
国内免费 | 14篇 |
出版年
2023年 | 282篇 |
2021年 | 536篇 |
2020年 | 432篇 |
2019年 | 473篇 |
2018年 | 1107篇 |
2017年 | 1131篇 |
2016年 | 1269篇 |
2015年 | 1473篇 |
2014年 | 1694篇 |
2013年 | 2694篇 |
2012年 | 4101篇 |
2011年 | 4513篇 |
2010年 | 2471篇 |
2009年 | 1831篇 |
2008年 | 3761篇 |
2007年 | 3892篇 |
2006年 | 3653篇 |
2005年 | 3367篇 |
2004年 | 3262篇 |
2003年 | 2949篇 |
2002年 | 2958篇 |
2001年 | 1782篇 |
2000年 | 1997篇 |
1999年 | 1175篇 |
1998年 | 708篇 |
1997年 | 505篇 |
1996年 | 559篇 |
1995年 | 485篇 |
1994年 | 528篇 |
1993年 | 476篇 |
1992年 | 540篇 |
1991年 | 477篇 |
1990年 | 424篇 |
1989年 | 413篇 |
1988年 | 391篇 |
1987年 | 409篇 |
1986年 | 349篇 |
1985年 | 458篇 |
1984年 | 511篇 |
1983年 | 456篇 |
1982年 | 462篇 |
1981年 | 427篇 |
1980年 | 363篇 |
1979年 | 361篇 |
1978年 | 358篇 |
1977年 | 351篇 |
1976年 | 319篇 |
1975年 | 360篇 |
1974年 | 317篇 |
1973年 | 292篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
1.
2.
The influence of fruit ingestion by the bat, Sturnira lilium, on germination of the seeds of the tree Solanum riparium was studied in a secondary rain forest in northwestern Argentina. Bat frequencies in disturbed areas were analyzed by mist net captures. Germination rates were determined for seeds collected from trees and bat feces. S. lilium was the most abundant fruit bat in the study area. Fruit digestion and the passage of seeds through the intestine did not significantly affect germination in S. riparium. In this case the fruit bats, therefore, probably provide only seed dispersal. 相似文献
3.
Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues. 相似文献
4.
Vernon Shattuck Frank R. Katterman 《Biochemical and biophysical research communications》1982,109(3):1017-1025
When cotyledonary tissue of cotton are treated with the mutagen ethyl methanesulfonate and then germinated, an enhanced, unscheduled DNA synthesis response is observed, along with a concomitant increase in the thymidine triphosphate precursor pool size. The implications of these results are discussed in this paper. 相似文献
5.
6.
7.
8.
In a section of the Liassic southwest of the village of Préjano (Prov. Logroño) Sinemurian Dasyclad algae were found for the first time in the “Bankkalk-Series” of the “Carniolas-Formation” which is not dated up to that time. Six species,Dissocladella lucasi (Cros & Lemoine),Dissocladella iberica nov. sp.,Dissocladella ebroensis nov. sp.,Sestrosphaera liasina Pia,Gyroporella retica (Zanin) andMacroporella nov. sp. aff. sturi Bystricky are described. 相似文献
9.
S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism. 相似文献
10.
Frank J. Turano Kenneth Glade Wilson 《In vitro cellular & developmental biology. Plant》1985,21(3):135-139
Summary The feasibility of using plant cell culture to measure toxicity was determined by investigating the toxicological effects
of three chemical compounds, allyl alcohol, propargylglycine, and cadmium chloride, on cell cultures ofCatharanthus roseus G. Don (Madagascar periwinkle). Suspension cultures ofC. roseus were maintained in modified B5 medium and transferred every 5 d. Five-day-old cell cultures were exposed to various concentrations
(10,3,1,0.3,0.1,0.03,0.01,0.003,0.001,0.0003,0.0001, 0.00003, and 0.0 mM) of the toxicants in both acute and chronic toxicity tests.
In the acute test, cells were exposed to the toxicant for 24 h, washed three times with sterile medium, and plated in petri
plates with an equal volume of 1.4% agar medium. Cells in the chronic test were plated with an equal volume of 1.4% agar medium
containing various concentrations of the toxicant. Cells were incubated 28 d at 30°C in the dark. The colonies were counted
and the results plotted as percent survival versus toxicant concentration. The results indicate, at the concentrations tested,
thatC. roseus assay may be feasible in that it fulfills the criteria for a practical assay (e.g., rapid, simple, quantifiable, and reproducible).
This work was submitted to the faculty of Miami University in partial fulfillment of the requirements for the degree of Master
of Environmental Science, Institute of Environmental Sciences. 相似文献