全文获取类型
收费全文 | 720841篇 |
免费 | 82903篇 |
国内免费 | 424篇 |
专业分类
804168篇 |
出版年
2018年 | 6246篇 |
2016年 | 8349篇 |
2015年 | 10710篇 |
2014年 | 13030篇 |
2013年 | 18568篇 |
2012年 | 20489篇 |
2011年 | 21204篇 |
2010年 | 14151篇 |
2009年 | 13169篇 |
2008年 | 18806篇 |
2007年 | 19714篇 |
2006年 | 18471篇 |
2005年 | 17846篇 |
2004年 | 17685篇 |
2003年 | 17177篇 |
2002年 | 16586篇 |
2001年 | 31627篇 |
2000年 | 32079篇 |
1999年 | 25490篇 |
1998年 | 8667篇 |
1997年 | 9122篇 |
1996年 | 8824篇 |
1995年 | 8385篇 |
1994年 | 8351篇 |
1993年 | 8154篇 |
1992年 | 21633篇 |
1991年 | 21419篇 |
1990年 | 21186篇 |
1989年 | 20621篇 |
1988年 | 19251篇 |
1987年 | 18512篇 |
1986年 | 17097篇 |
1985年 | 17493篇 |
1984年 | 14486篇 |
1983年 | 12655篇 |
1982年 | 9549篇 |
1981年 | 8893篇 |
1980年 | 8365篇 |
1979年 | 14136篇 |
1978年 | 10977篇 |
1977年 | 10123篇 |
1976年 | 9661篇 |
1975年 | 10885篇 |
1974年 | 11369篇 |
1973年 | 11219篇 |
1972年 | 10411篇 |
1971年 | 9255篇 |
1970年 | 8122篇 |
1969年 | 7601篇 |
1968年 | 7060篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The cytomegalovirus enhancer: a pan-active control element in transgenic mice. 总被引:41,自引:2,他引:39 下载免费PDF全文
In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney. 相似文献
992.
993.
We present a fast, reliable and inexpensive restriction-free cloning method for seamless DNA insertion into any plasmid without sequence limitation. Exponential megapriming PCR (EMP) cloning requires two consecutive PCR steps and can be carried out in one day. We show that EMP cloning has a higher efficiency than restriction-free (RF) cloning, especially for long inserts above 2.5 kb. EMP further enables simultaneous cloning of multiple inserts. 相似文献
994.
The presence of the t haplotypes in strains derived from the Japanese wild mice (Mus musculus molossinus) was investigated. Crosses between the T/+ heterozygous short tailed mice and five normal tailed molossinus strains (MOL-ANJ, MOA, MOL-NEM, MOM and Mns) produced no tailless mice, indicating that these strains possess no t haplotype. In contrast, tailless mice were produced by a cross between the T/+ heterozygotes and a MOL-NIS strain. Mating experiments showed that the tailless character was due to an interaction between the T gene and an autosomal recessive gene carried by the MOL-NIS strain that expresses the short tail character under the homozygous condition. We have tentatively named this gene brachyury-interacting tail length modifier (btm). It remains to be investigated whether the btm gene is located in the t complex region or in the other locus. 相似文献
995.
Bacillus thuringiensis serotype H-14 spores and crystals, produced in 51 fermenters, were centrifuged and resuspended in emulsified palm olein to give 3.2 x 10(11) colony forming units (cfu)/ml. The suspension was mixed with a cassava-molasses-palm olein-charcoal (CMPC-2) mixture which served as the carrier, adhesive, dispersant and protectant. The final concentration of the formulation was 3.2 x 10(9) cfu/ml. The lethal concentrations capable of killing 50% of the test population (LC50) of CMPC-2 during 0, 1 and 2 years of storage at 32 +/- 4 degrees C were 0.056, 0.058 and 0.058 mg/ml respectively as against 0.054, 0.051 and 0.054 mg/ml for the Institut Pasteur Standard-1978 (IPS-78) during the corresponding period. The chi 2 tests showed that the results were homogeneous at P = 0.05. The relative potencies of the preparations were 964.3, 879.3 and 931 International toxic units (ITU) Aedes aegypti as compared with the 1000 ITU assigned to IPS-78. At 95% confidence limits there was no significant difference between the potencies of CMPC-2 and IPS-78. Field tests showed that CMPC-2 provided between 87.5 and 100% control of natural populations of Aedes spp. and Cutex spp. Sedimentation tests showed that CMPC-2 settled markedly during storage. This, therefore, required that the product be thoroughly shaken before use. 相似文献
996.
A Saadawi A Ayad V N Maltsev 《Journal of hygiene, epidemiology, microbiology, and immunology》1991,35(3):241-249
In the course of research done it was concluded that circulation of pool water through the nuclear reactor core produces a bactericidal effect on microflora due to influence of radiation of various types. Contents of microbes returns to the initial level after 2-4 months after circulation was stopped. Microflora of pool water comprises big amount of coccus, G-positive rods and fungi and a lower content of G-negative rods if compared to water which had been used to fill reactor pool. There is an increased number of radioresistant forms with intensified production of catalase and nuclease. Supposedly, presence of these enzymes gives to the microbes certain advances to survive in high-radiation zones. 相似文献
997.
Catherine E. Rogers Karl R. Mattox Kenneth D. Stewart 《American journal of botany》1980,67(5):774-783
Chlorokybus atmophyticus has a sarcinoid growth habit and produces scale-covered zoospores. Flagella are laterally inserted and attached internally to a multilayered structure characteristic of the Charophyceae. There are two kinds of pyrenoid in each cell, a feature previously observed in only one scaly green flagellate. C. atmophyticus demonstrates that the sarcinoid growth habit arose independently at least twice in the green algae and cannot be used to define taxonomic groups unless combined with other criteria. It is further concluded that C. atmophyticus should be classified in a separate family Chlorokybaceae and a separate order Chloroky bales. 相似文献
998.
P Demol R Palma J J Bernier 《Archives internationales de physiologie et de biochimie》1980,88(3):237-240
In the conscious rat the increasing distension of the colon (from 2 to 6 ml) induced a slight decrease of exocrine pancreatic secretion which was more important for protein output than for volume. Nevertheless this inhibitory effect was never significant even with the important distension of 6 ml which induced a visible uneasiness in the animal. 相似文献
999.
1000.
The products of mitochondrial protein synthesis have been investigated in Tetrahymena after labelling with [35S]methionine in the presence of cycloheximide. The labelled proteins were analyzed by sodium dodecyl sulfate slab polyacrylamide gel electrophoresis. We have identified 13 electrophoretically discrete bands as well as 4 other bands with a more variable occurrence. These proteins ranged in apparent molecular weight from 8100 to 57,500. The cycloheximide-resistant incorporation could be blocked with chloramphenicol. The mitochondrial proteins appeared to be in a disaggregated state and were stable to agents such as trichloroacetic acid (hot or cold) and chloroform-methanol. The pattern of proteins was similar following labelling times ranging from 30 min to 3 h. 相似文献