全文获取类型
收费全文 | 3085篇 |
免费 | 158篇 |
国内免费 | 3篇 |
专业分类
3246篇 |
出版年
2022年 | 12篇 |
2021年 | 21篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 36篇 |
2017年 | 29篇 |
2016年 | 45篇 |
2015年 | 67篇 |
2014年 | 87篇 |
2013年 | 241篇 |
2012年 | 144篇 |
2011年 | 174篇 |
2010年 | 101篇 |
2009年 | 109篇 |
2008年 | 177篇 |
2007年 | 190篇 |
2006年 | 216篇 |
2005年 | 204篇 |
2004年 | 198篇 |
2003年 | 197篇 |
2002年 | 193篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 32篇 |
1998年 | 32篇 |
1997年 | 43篇 |
1996年 | 39篇 |
1995年 | 50篇 |
1994年 | 32篇 |
1993年 | 44篇 |
1992年 | 39篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 12篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 26篇 |
1979年 | 10篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有3246条查询结果,搜索用时 0 毫秒
21.
As a quantitative approach to the life histories of fishes, the present paper attempted to predict a relation among reproduction, growth and mortality numerically with a technique of control theory, the discrete maximum principle. A method for predicting the relation was derived on the postulate that natural selection maximized the net reproductive rate subject to a few constraints. The derived method was applied to Atlantic cod and Atlantic herring populations in the Southern Gulf of St. Lawrence as numerical examples. The examples demonstrated that the theoretical reproductive effort and body weight were well consistent with the observed ones every age but the theoretical survival rates were slightly different from the observed ones. For the reasons mentioned below, however, it should be interpreted that the examples rather support the adopted postulate to a certain degree. First, in general, it is very difficult to obtain good estimates of the rates with traditional methods. Second, intense fishing pressure possibly changes the life history parameters to some extent in fish populations. Moreover, the examples also suggested that, to examine the postulate in further detail, similar analyses had to be made with the data of many fish populations on which intense fishing pressure had not been exerted. 相似文献
22.
23.
Tetsuya Tosa Tadashi Sato Takao Mori Yuhsi Matuo Ichiro Chibata 《Biotechnology and bioengineering》1973,15(1):69-84
Various methods were tried for the immobilization of aspartase, and the preparation having the highest activity was obtained when partially purified aspartase from Escherichia coli was entrapped into polyacrylamide gel Iattice. Enzymatic properties of the immobilized aspartase were investigated and compared with those of the native aspartase. With regard to optimum pH, temperature, concentration of Mn++, kinetic constants and heat stability, no marked difference was observed between the native and immobilized aspartases. By employing an enzyme column packed with the immobilized aspartase, conditions for continuous production of L -aspartic acid from ammonium fumarate were investigated. When a solution of 1M ammonium fumarate (pH 8.5, containing 1mM MnCl2) was passed through the aspartase column at the flow rate of SV = 0.08 at 37°C, the highest rate of reaction was attained. From the column effluents, L-aspartic acid was obtained in a good yield. 相似文献
24.
Exchange of Genetic Material between Salmonella Typhimurium and Escherichia Coli K-12 总被引:10,自引:0,他引:10 下载免费PDF全文
Tadashi Miyake 《Genetics》1962,47(8):1043-1052
25.
FINE STRUCTURE OF SPINY SPORES OF STREPTOMYCES 总被引:1,自引:0,他引:1
26.
ELECTRON MICROSCOPY OF VIRUS-INFECTED YEAST CELLS 总被引:1,自引:0,他引:1
27.
The Large Isoform of Myelin-Associated Glycoprotein Is Scarcely Expressed in the Quaking Mouse Brain
Nobuya Fujita Shuzo Sato Hideaki Ishiguro Takashi Inuzuka Hiroko Baba Tadashi Kurihara Yasuo Takahashi Tadashi Miyatake 《Journal of neurochemistry》1990,55(3):1056-1059
Two polypeptide isoforms of myelin-associated glycoprotein (MAG) with molecular masses of 72 and 67 kDa are produced by alternative splicing of the exon 12 portion. Our previous work has demonstrated that in the quaking mouse brain this alternative splicing is lacking and that the mRNA coding the large MAG isoform (L-MAG) is scarcely expressed, whereas that of small MAG isoform (S-MAG) is overexpressed. In the present study, we prepared antisera specific to the S-MAG and L-MAG amino acid residues, respectively. Immunoblots showed that the L-MAG band was scarcely detectable in the quaking mouse brain, whereas the S-MAG band had an apparently higher molecular mass than in the normal control. Our immunohistochemical study also showed that L-MAG was scarcely stained in the quaking mouse brain. These results seemed to reflect a reduction in content of L-MAG mRNA and abnormal glycosylation in the quaking mouse brain. 相似文献
28.
Yutaka Nagata Hiroshi Ebisu Masao Tamaru Kimikazu Fujita Tadashi Koide 《Journal of neurochemistry》1989,52(5):1570-1575
We found atrial natriuretic peptide (ANP), known as a humoral factor in regulating body fluid volume and blood pressure, in considerable quantities in rat superior cervical sympathetic ganglion (SCG) by radioimmunoassay after separation with reverse-phase HPLC. Although the ANP content of the immature rat 1 week after birth was low, it doubled at 2 weeks and then increased gradually, until it reached the adult level. Denervation caused a rapid decrease in the ANP content to half of the intact SCG level after 3 h, which then fell to 10% of the control value on day 2 after operation. The time course of ANP content reduction after denervation was similar but rather faster than that of activity of the acetylcholine-synthesizing enzyme, choline acetyltransferase, an observation suggesting that ANP may partly contribute to cholinergic synaptic transmission. On the other hand, axotomy produced a rather slower decrease in the ANP content than did denervation. Enucleation and sialoadenectomy also caused a considerable reduction of the ANP content. Thus, part of the ANP found in the ganglion is apparently transported from sympathetically innervated extraganglionic organs via retrograde axoplasmic flow. 相似文献
29.
Ken-ichi Ishiwata Tadashi Suzuki Satoru Iwamori Setsuo Yoshino Nobuyoshi Makiguchi 《Biotechnology letters》1990,12(3):185-190
Summary The tryptophan synthase genes,trpA andtrpB, from a moderate thermophile,Bacillus
stearothermophilus IFO13737, were expressed efficiently inEscherichia
coli. The recombinant tryptophan synthase amounted to 22% of the soluble cellular protein, and was purified to homogeneity by three steps. The enzyme is more thermostable thanE.coli tryptophan synthase, especially the subunit. The enzyme is also more resistant to sodium dodecylsulfate and methanol thanE.coli enzyme. 相似文献
30.
Duško Ili? Satoshi Kanazawa Yasuhide Furuta Tadashi Yamamoto Shinichi Aizawa 《Experimental cell research》1996,222(2):298
Focal adhesion kinase (FAK) is a novel nonreceptor protein tyrosine kinase that localizes in focal adhesions. It is expressed in a variety of cell types, and we reported earlier that its deficiency causes a decrease of mobility in mesodermal cells with enhanced formation of focal adhesions. With embryoid bodies generated from embryonic stem cells, we also observed a decrease of mobility in FAK-deficient endodermal cells with enhanced focal adhesion formation. 相似文献