全文获取类型
收费全文 | 146276篇 |
免费 | 150241篇 |
国内免费 | 45752篇 |
出版年
2022年 | 3921篇 |
2021年 | 4895篇 |
2020年 | 4370篇 |
2019年 | 6402篇 |
2018年 | 5432篇 |
2017年 | 4762篇 |
2016年 | 5412篇 |
2015年 | 6538篇 |
2014年 | 8203篇 |
2013年 | 7998篇 |
2012年 | 9894篇 |
2011年 | 10240篇 |
2010年 | 10006篇 |
2009年 | 14726篇 |
2008年 | 9392篇 |
2007年 | 8753篇 |
2006年 | 7518篇 |
2005年 | 6648篇 |
2004年 | 5832篇 |
2003年 | 5063篇 |
2002年 | 5355篇 |
2001年 | 6301篇 |
2000年 | 3885篇 |
1999年 | 7809篇 |
1998年 | 9424篇 |
1997年 | 9490篇 |
1996年 | 8806篇 |
1995年 | 9053篇 |
1994年 | 8415篇 |
1993年 | 8049篇 |
1992年 | 8065篇 |
1991年 | 8067篇 |
1990年 | 8823篇 |
1989年 | 8055篇 |
1988年 | 7327篇 |
1987年 | 6460篇 |
1986年 | 5949篇 |
1985年 | 5363篇 |
1984年 | 4154篇 |
1983年 | 3351篇 |
1982年 | 3692篇 |
1981年 | 3307篇 |
1980年 | 3193篇 |
1979年 | 3322篇 |
1978年 | 3029篇 |
1977年 | 2944篇 |
1976年 | 2771篇 |
1973年 | 2529篇 |
1972年 | 2859篇 |
1971年 | 2616篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
143.
L. G. Akhmetzyanova A. A. Saveliev S. Yu. Selivanovskaya 《Contemporary Problems of Ecology》2012,5(6):554-558
This paper presents an algorithm for determining the content of oil products in remediated soil that is safe for plants and microorganisms. The algorithm includes laboratory modeling of the remediation of soil samples that contain different amounts of soil products, determination of the biological parameters that provide the integral characterization of the soil state in these samples, and analysis of the results on the basis of odds-ratio statistics, which allows one to determine the content of oil products, starting from which the state of an oil-contaminated soil has no significant difference from a control soil. 相似文献
144.
145.
Genetic and morphological characterization of ftsB and nrdB mutants of Escherichia coli. 总被引:11,自引:8,他引:3
The ftsB gene of Escherichia coli is believed to be involved in cell division. In this report, we show that plasmids containing the nrdB gene could complement the ftsB mutation, suggesting that ftsB is an allele of nrdB. We compared changes in the cell shape of isogenic nrdA, nrdB, ftsB, and pbpB strains at permissive and restrictive temperatures. Although in rich medium all strains produced filaments at the restrictive temperature, in minimal medium only a 50 to 100% increase in mean cell mass occurred in the nrdA, nrdB, and ftsB strains. The typical pbpB cell division mutant also formed long filaments at low growth rates. Visualization of nucleoid structure by fluorescence microscopy demonstrated that nucleoid segregation was affected by nrdA, nrdB, and ftsB mutations at the restrictive temperature. Measurements of beta-galactosidase activity in lambda p(sfiA::lac) lysogenic nrdA, nrdB, and ftsB mutants in rich medium at the restrictive temperature showed that filamentation in the nrdA mutant was caused by sfiA (sulA) induction, while filamentation in nrdB and ftsB mutants was sfiA independent, suggesting an SOS-independent inhibition of cell division. 相似文献
146.
Elena C. Guzman Alfonso Jimenez-Sanchez Elisha Orr Robert H. Pritchard 《Molecular & general genetics : MGG》1988,212(2):203-206
Summary A temperature shift-up accompanied by a reduction in RNA polymerase activity in Escherichia coli causes an increased rate of initiation leading to a 1.7- to 2.2-fold increase in chromosome copy number. A temperature shift-up without a reduction in polymerase activity induces only a transient non-scheduled initiation of chromosome replication caused by heat shock with no detectable effect on chromosome copy number. 相似文献
147.
Procedure and Analysis of a Useful Method in Determining Mycelial Dry Weights from Agar Plates
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The evaluation of growth by dry weight determination of fungus mycelium for agar plates was examined. The data obtained were statistically analyzed. This method was shown to be sufficiently accurate to be used as an investigative tool. 相似文献
148.
Heat treatment results in a loss of transgene-encoded activities in several tobacco lines. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C. 相似文献
149.
The cdc6 mutants of Schizosaccharomyces pombe have been classified as being defective in progression through the G2 phase of the cell cycle. We cloned an S. pombe gene that could complement the temperature-sensitive growth of the cdc6-23 mutant. Unexpectedly, the cloned gene was allelic to pol3, which encodes the catalytic subunit of DNA polymerase δ. Integration mapping confirmed that cdc6 and pol3 are identical. The cdc6-23 mutant carries one amino acid substitution in the conserved N3 region of Pol3.
Received: 17 October 1996 / Accepted: 19 November 1996 相似文献
150.