全文获取类型
收费全文 | 112176篇 |
免费 | 1365篇 |
国内免费 | 916篇 |
专业分类
114457篇 |
出版年
2023年 | 139篇 |
2022年 | 318篇 |
2021年 | 501篇 |
2020年 | 327篇 |
2019年 | 306篇 |
2018年 | 12204篇 |
2017年 | 11006篇 |
2016年 | 7992篇 |
2015年 | 1459篇 |
2014年 | 1234篇 |
2013年 | 1634篇 |
2012年 | 5606篇 |
2011年 | 13989篇 |
2010年 | 12690篇 |
2009年 | 8846篇 |
2008年 | 10587篇 |
2007年 | 12144篇 |
2006年 | 1022篇 |
2005年 | 1169篇 |
2004年 | 1597篇 |
2003年 | 1588篇 |
2002年 | 1271篇 |
2001年 | 662篇 |
2000年 | 539篇 |
1999年 | 325篇 |
1998年 | 171篇 |
1997年 | 156篇 |
1996年 | 131篇 |
1995年 | 140篇 |
1994年 | 138篇 |
1993年 | 140篇 |
1992年 | 270篇 |
1991年 | 266篇 |
1990年 | 238篇 |
1989年 | 229篇 |
1988年 | 204篇 |
1987年 | 192篇 |
1986年 | 168篇 |
1985年 | 191篇 |
1984年 | 212篇 |
1983年 | 148篇 |
1982年 | 133篇 |
1981年 | 126篇 |
1980年 | 111篇 |
1979年 | 163篇 |
1978年 | 119篇 |
1977年 | 105篇 |
1974年 | 127篇 |
1972年 | 355篇 |
1971年 | 367篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Summary A child with cri-du-chat syndrome, 46,XY,5p-, was born to a mother who had two normal children and two abortuses. The mother was shown to carry a balanced translocation. Giemsa and fluorescent banding demonstrate the exact location of the translocated segment. The deleted short arm of chromosome number 5 was shown to be attached to the long arm of chromosome number 11.
We are indeed indebted to Dr. G. R. Hennigar for facilities and Dr. C. D. Barnett for financial assistance. 相似文献
Zusammenfassung Ein Kind mit Cri-du-chat Syndrom und Karyotyp 46,XY,5p- wurde von einer Mutter geboren, die zuvor zwei gesunde Kinder und zwei Aborte gehabt hatte. Bei der Mutter wurde eine balancierte Translokation nachgewiesen; Chiemsa- und Fluorescens-Bandenmuster zeigten die genaue Lokalisation des translozierten Segmentes: Der deletierte kurze Arm des Chromosoms Nr.5 war an den langen Arm vom Chromosom Nr. 11 angeheftet.
We are indeed indebted to Dr. G. R. Hennigar for facilities and Dr. C. D. Barnett for financial assistance. 相似文献
32.
Frankia is the diverse bacterial genus that fixes nitrogen within root nodules of actinorhizal trees and shrubs. Systematic and ecological
studies of Frankia have been hindered by the lack of morphological, biochemical, or other markers to readily distinguish strains. Recently,
nucleotide sequence of 16 S RNA from the small ribosomal subunit has been used to classify and identify a variety of microorganisms.
We report nucleotide sequences from portions of the 16 S ribosomal RNA from Frankia strains AcnI1 isolated from Alnus viridis ssp. crispa (Ait.) Turrill and PtI1 isolated from Purshia tridentata (Pursh) DC. The number of nucleotide base substitutions and gaps we find more than doubles the previously reported sequence
diversity for the same variable regions within other strains of Frankia. 相似文献
33.
A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog
1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication
rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in
a solution of indole-3-butyric acid (IBA -3 mg l−1) and 1-naphthaleneacetic acid (NAA-1 mg l−1) at 5°C. 相似文献
34.
35.
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
36.
For estimation of growth, the efficiency of linked cross sectional scheme has been compared with pure longitudinal and cross sectional schemes. The relevant estimation theory has been developed and the expressions for the optimum estimators alongwith their variances have been derived. It has been observed that for estimation of growth, the linked cross-sectional scheme has been observed to be less efficient as compared to pure longitudinal scheme but more efficient than pure cross-sectional scheme. 相似文献
37.
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
38.
39.
40.
A K Srivastava C Pandey K P Dwivedi V K Singh 《Indian journal of biochemistry & biophysics》1989,26(3):199-200
QSAR studies have been performed on the homologues of 3-triazines, using molecular connectivity index and van der Waal volume as structural parameters. The regression analysis has shown good correlation between antitumour activity and the two structural parameters. 相似文献