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21.
David Jackson 《BMJ (Clinical research ed.)》1989,298(6675):753-754
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R H Jackson 《BMJ (Clinical research ed.)》1976,1(6003):220-221
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25.
Hanafi H. Russell Richard J. Jackson David P. Spath Steven A. Book 《The Western journal of medicine》1987,147(5):615-622
Drinking water contamination by toxic chemicals has become widely recognized as a public health concern since the discovery of 1,2-dibromo-3-chloropropane in California''s Central Valley in 1979. Increased monitoring since then has shown that other pesticides and industrial chemicals are present in drinking water. Contaminants of drinking water also include naturally occurring substances such as asbestos and even the by-products of water chlorination. Public water systems, commercially bottled and vended water and mineral water are regulated, and California is also taking measures to prevent water pollution by chemicals through various new laws and programs. 相似文献
26.
Genetic control of capsid length in bacteriophage T4: clustering of ptg mutations in gene 23. 总被引:1,自引:1,他引:0 下载免费PDF全文
Fifty-two new bacteriophage T4 ptg mutations have been isolated by selecting for the giant-capsid phenotype they display. Genetic mapping placed all of them at eight sites, all located in gene 23. These sites were clustered in three locations, one near amber B17 (gene 23 nucleotide [NT] 268), another centrally placed between amE506 (NT 706) and amE1270 (NT 925), and the third between amC208 (NT 1297) and amE1236 (NT 1489). The lack of a selective system for identifying recombinant genotypes when dealing with the very close linkages found within these clusters opens the possibility that more than eight sites are represented in this set of mutations. Since one site was represented by only one mutation, it seems likely that further searching might uncover additional sites. It is suggested that the clustering of mutations observed here identifies regions of the gene 23 product that play a role in regulating the capsid length of T4. 相似文献
27.
Nitrogen Enhancement of Phosphate Transport in Roots of Zea mays L. : I. Effects of Ammonium and Nitrate Pretreatment 总被引:1,自引:0,他引:1 下载免费PDF全文
The effect of nitrogen status on phosphorous uptake and translocation was examined in 6-day-old dark-grown decapitated maize seedlings exposed to 25 micromolar phosphorous. Transfer to complete solutions containing 1 millimolar ammonium resulted in an increase in phosphorous uptake rate after 6 to 8 hours. The stimulus remained effective for at least 5.5 hours upon subsequent transfer to nitrogen-free solutions. Pretreatments for 16 hours with either nitrate or ammonium resulted in enhanced rates of subsequent phosphorous uptake and in enhanced translocation to the xylem of the exogenously supplied phosphorous. Both processes reached a plateau following pretreatment with 0.1 to 1.0 millimolar concentrations of either nitrogen ion. Further enhancement occurred with 10 millimolar nitrate, but not with 10 millimolar ammonium pretreatment. Although nitrogen pretreatments slightly increased the quantity of exogenous phosphorous retained in the root tissue, most of the extra phosphorous taken up by the nitrogen-pretreated seedlings was translocated to the xylem. The enhanced translocation, however, did not totally account for the increase in uptake implying a specific stimulation of the uptake process. 相似文献
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Overexpression and DNA-binding properties of the mer-encoded regulatory protein from plasmid NR1 (Tn21). 总被引:13,自引:10,他引:3 下载免费PDF全文
A Heltzel D Gambill W J Jackson P A Totis A O Summers 《Journal of bacteriology》1987,169(7):3379-3384
In plasmid NR1 the expression of genes involved in mercury resistance (Tn21) is regulated by the trans-acting product of the merR gene. An in vivo T7 RNA polymerase-promoter overexpression system was used to detect a protein of approximately 16,000 daltons encoded by the merR reading frame. Overexpressed MerR constituted about 5% of labeled proteins. An in vitro MerR-mer-op (mer-op is the mer operator and promoter region) gel electrophoresis binding assay established that the binding site for MerR was located between the putative -35 and -10 sequences of the promoter for the mer structural genes. A nonsense mutation in the carboxyl half of MerR resulted in the loss of biological function and the loss of in vitro mer-op binding properties. 相似文献
30.
I Wilkinson C J Jackson G M Lang V Holford-Strevens A H Sehon 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(2):326-331
The specific tolerance induced in mice by conjugates of human monoclonal IgG (HIgG) with monomethoxypolyethylene glycol (mPEG) was transferred to normal mice by spleen cells or a surface immunoglobulin negative (sIg-) Lyt-2+ subpopulation of these cells. Although transferable tolerance was demonstrable 6 to 14 days after treatment of the cell donors with tolerogen, the state of tolerance persisted in the treated mice for at least 43 days. Moreover, an extract prepared by freezing and thawing of the sIg- spleen cells obtained from mice 6 days after treatment with HIgG(mPEG)20 was capable of reducing (greater than 85%) the immune response of normal mice to heat aggregated HIgG. On the basis of these results, it is suggested that similar tolerogenic mPEG derivatives of xenogeneic monoclonal immunoglobulins (XIg) may prove to be useful therapeutic agents in man when administered before treatment with the unmodified XIg. 相似文献