全文获取类型
收费全文 | 121917篇 |
免费 | 2453篇 |
国内免费 | 890篇 |
专业分类
125260篇 |
出版年
2023年 | 157篇 |
2022年 | 148篇 |
2021年 | 349篇 |
2020年 | 288篇 |
2019年 | 297篇 |
2018年 | 12283篇 |
2017年 | 11080篇 |
2016年 | 8160篇 |
2015年 | 1883篇 |
2014年 | 1565篇 |
2013年 | 2162篇 |
2012年 | 6352篇 |
2011年 | 14776篇 |
2010年 | 13116篇 |
2009年 | 9176篇 |
2008年 | 11481篇 |
2007年 | 12967篇 |
2006年 | 1869篇 |
2005年 | 2092篇 |
2004年 | 2437篇 |
2003年 | 2337篇 |
2002年 | 1975篇 |
2001年 | 902篇 |
2000年 | 763篇 |
1999年 | 549篇 |
1998年 | 264篇 |
1997年 | 225篇 |
1996年 | 192篇 |
1995年 | 186篇 |
1994年 | 158篇 |
1993年 | 169篇 |
1992年 | 318篇 |
1991年 | 336篇 |
1990年 | 271篇 |
1989年 | 216篇 |
1988年 | 229篇 |
1987年 | 199篇 |
1986年 | 182篇 |
1985年 | 175篇 |
1984年 | 166篇 |
1983年 | 141篇 |
1982年 | 133篇 |
1981年 | 150篇 |
1979年 | 168篇 |
1978年 | 160篇 |
1976年 | 127篇 |
1975年 | 117篇 |
1974年 | 132篇 |
1972年 | 324篇 |
1971年 | 390篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Chien-Hung Liu Wen-Ming Chen Jo-Shu Chang 《World journal of microbiology & biotechnology》2007,23(5):633-640
Acidic lipase finds its commercial values in medical applications and bioremediation of food wastes. In this work, approaches
for rapid screening of lipase-producing bacteria were developed and the feasibility assessment of the screening methods was
performed. From food waste samples, the proposed screening procedures allowed isolation of sixteen pure bacterial strains
expressing higher lipase activity at acidic pH (pH 6.0) than at alkaline pH (pH 9.0). To enhance the accuracy of lipase activity
determination under acidic conditions, a novel assay procedure was also developed by deactivating lipase activity by microwave
treatment prior to back titration. This additional step could minimize interferences arising from residual lipase activity
during conventional direct back-titration methods in measuring lipase activity at acidic pH. Using the four strategies proposed
in this work, the best acidic-lipase-producing isolate was obtained by strategy C (SSC) and was identified as Aeromonas sp. C14, displaying an optimal lipase activity of 0.7 U/ml at an acidic pH of 6.0. 相似文献
52.
Takahiro Ishii Tatsufumi Okino Yosuke Mino Hiroaki Tamiya Fuyuhiko Matsuda 《Plant Growth Regulation》2007,52(2):131-139
Starfish waste has been shown to be an effective compost material not only in the promotion of plant growth but also in terms
of having insecticidal activity. In the present study, plant growth regulation by chemicals from starfish was examined. The
aqueous fraction from a hot water extract of the starfish Asterias amurensis Lütken showed plant-growth activity, while the aqueous fraction from a methanol extract inhibited growth of Brassica campestris. The lipophilic fraction from the methanol extract also exhibited a plant growth-promoting effect. The active components
from each extract were identified. Asterubine from the hot water extract promoted plant growth. A ceramide from the lipophilic
fraction showed root growth promoting effect, and three glucocerebrosides had promotive effects on the entire plant. Asterosaponins
were identified as the main growth inhibitors in the aqueous fraction of the methanol extract. These active compounds from
starfish waste could be analyzed as potential plant growth regulators in agricultural applications in the future. 相似文献
53.
54.
55.
Cultured cells from the anterior pituitary glands of adult rats were treated with the tripeptide aldehyde proteinase inhibitor, BOC-DPhe-Phe-Lys-H. The addition of this tripeptide aldehyde decreased the in vitro release of prolactin to 25% of the control value, while the release of growth hormone in the same cultures decreased to 33% of the control value. Prolactin immunostaining was stronger in semithin sections of proteinase-inhibitor-treated cultures than in control sections. After 2 h treatment with the inhibitor, prolactin- and growth hormone-containing secretory granules were numerous, and the number of crinophagic vacuoles had increased. In the presence of the inhibitor, the overall cytoarchitecture of parenchymal cells was well preserved, and the pathway of the uptake of cationic ferritin appeared to be unaffected. 相似文献
56.
Methyl 3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranoside (6) was synthesized through two routes in five steps from methyl 2,3-anhydro-4-deoxy-β-dl-erythro-pentopyranoside (1). The first route proceeded via selective azide displacement of the 3-tosyloxy group of methyl 4-deoxy-2,3-di-O-tosyl-α-dl-threo-pentopyranoside, followed by detosylation and benzoylation. The second route consisted, with a better overall yield, in the azide displacement of the mesyloxy group of methyl O-benzoyl-4-deoxy-3-O-methylsulfonyl-α-dl-threo-pentopyranoside (10), obtained by benzylate opening of 1, followed by benzoylation, debenzylation, and mesylation. Compound 6 was transformed into its glycosyl chloride, further treated by 6-chloropurine to give the nucleoside 9-(3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranosyl)-6-chloropurine (13). When treated with propanolic ammonia, 13 yielded 9-(3-azido-3,4-dideoxy-β-dl-erythro-pentopyranosyl)adenine. 相似文献
57.
58.
Covalent dimerization of the adrenocorticotropin fragment ACTH11-24 increases its antagonistic potency on the ACTH-induced steroidogenesis in isolated bovine fasciculata/reticularis cells by 3 orders of magnitude when the C-termini are linked via a 10 A long spacer. This strong potentiation, probably mediated by cross-linking of the receptors, was shown to be dependent on the point of attachment of the monomeric fragment to the spacer, thus providing information about the position of the binding site in the hormonal segment and about the distance of the receptors on the cell surface. 相似文献
59.
60.