首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   12416篇
  免费   854篇
  国内免费   5篇
  13275篇
  2023年   81篇
  2022年   92篇
  2021年   205篇
  2020年   153篇
  2019年   173篇
  2018年   289篇
  2017年   246篇
  2016年   350篇
  2015年   595篇
  2014年   625篇
  2013年   836篇
  2012年   943篇
  2011年   917篇
  2010年   562篇
  2009年   474篇
  2008年   738篇
  2007年   726篇
  2006年   643篇
  2005年   630篇
  2004年   606篇
  2003年   547篇
  2002年   476篇
  2001年   229篇
  2000年   172篇
  1999年   160篇
  1998年   102篇
  1997年   85篇
  1996年   69篇
  1995年   71篇
  1994年   56篇
  1993年   56篇
  1992年   87篇
  1991年   72篇
  1990年   79篇
  1989年   72篇
  1988年   60篇
  1987年   53篇
  1986年   47篇
  1985年   63篇
  1984年   58篇
  1983年   43篇
  1982年   46篇
  1981年   56篇
  1979年   64篇
  1978年   65篇
  1976年   40篇
  1975年   35篇
  1974年   49篇
  1973年   35篇
  1971年   44篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
A series of new chiral thiosemicarbazones derived from homochiral amines in both enantiomeric forms were synthesized and evaluated for their in vitro antiproliferative activity against A549 (human alveolar adenocarcinoma), MCF‐7 (human breast adenocarcinoma), HeLa (human cervical adenocarcinoma), and HGC‐27 (human stomach carcinoma) cell lines. Some of compounds showed inhibitory activities on the growth of cancer cell lines. Especially, compound 17b exhibited the most potent activity (IC50 4.6 μM) against HGC‐27 as compared with the reference compound, sindaxel (IC50 10.3 μM), and could be used as a lead compound to search new chiral thiosemicarbazone derivatives as antiproliferative agents. Chirality 27:177–188, 2015. © 2014 Wiley Periodicals, Inc.  相似文献   
12.
Monoclonal antibodies were produced to electrophoretically pure hydrogenase fromThiocapsa roseopersicina. Protein immunoelectroblotting was used to identify the hydrogenase-specific antibodies. Among the 18 monoclonal antibodies selected by enzyme immunoassay, three were found to react with highly immunogenic trace contaminating proteins. One cell line produced antibody that inhibitied hydrogenase activity. This was the first specific inhibitor of the hydrogenase function. The results suggest that monoclonal antibodies could provide valuable new informations about the enzyme structure as well.  相似文献   
13.
14.
A major haemophiliac A, 27 years old, has been treated during 30 months, with high dosage of imported Factor VIII, in order to reduce the titer of a F VIII antibody. A good clinical result has been obtained. No sign of immunodeficiency has been observed. Normal values were obtained for T4/T8, ratio B2 microglobulin and no antibody was detected against the LAV virus isolated from cases of AIDS.  相似文献   
15.
Remains of two large sarcopterygians are described from Famennian deposits in Belgium. One of them is referred to Eusthenodon wängsjöi Jarvik; it is the first occurrence of this genus in Belgium. The other, much larger one, appears to be a tristichopterid. It has a postspiracular; size and shape of the mandible similar to those of Platycephalichthys skuenicus and P. bischoffi ; snout and cheek patterns close to those of Eusthenodon ; unusual shape of the supratemporal resembling that of Hyneria , Mandageria and Platycephalichthys skuenicus ; and tooth histology quite similar to that of Eusthenodon and Platycephalichthys .  相似文献   
16.
To determine if human XX maleness results from an abnormal chromosomal X-Y interchange, we studied the inheritance of the paternal pseudoautosomal region in nine patients. Those six patients in whom Y-specific DNA was found (Y(+)) inherited the entire pseudoautosomal region from the paternal Y chromosome and lost that of the paternal X chromosome. Moreover, in three Y(+) cases, we observed the deletion of a paternal Xp locus tightly linked to the pseudoautosomal region. These results definitively show that an abnormal and terminal X-Y interchange during paternal meiosis causes Y(+)XX maleness. In contrast, no abnormal X-Y interchange was observed in any of the three Y(-) cases analyzed, suggesting that maleness can occur in the absence of any Y-specific DNA.  相似文献   
17.
Antibody responses of young adults to Haemophilus influenzae type b polysaccharide (Hib) or its protein conjugate were studied with special attention to the isotype composition of the antibodies. Three conclusions of interest can be made: 1) Immunoglobulin G (IgG) antibodies in polysaccharide-immunized volunteers displayed the subclass pattern previously found in antibodies to meningococcal type A polysaccharide. IgG1 was the predominant subclass in IgG antibodies of some individuals, IgG2 in others. Still others had the two subclasses in varying but more even proportions. 2) The conjugate vaccine induced a geometric mean response 2 to 3 times higher and an IgG response 4 times higher to Hib than the polysaccharide vaccine. 3) Anti-Hib antibodies induced by the conjugate vaccine still had essentially the same IgG subclass composition as anti-Hib antibodies induced by the polysaccharide. This composition was strikingly different from the composition of the anti-diphtheria toxoid response induced by the same conjugate vaccine.  相似文献   
18.
Anti-messenger oligodeoxynucleotides covalently linked to an intercalating agent were tested for their ability to inhibit translation of Trypanosoma brucei mRNAs in a cell-free system. The sequence of these oligodeoxynucleotides was complementary to part of the 35-nucleotide (nt) sequence which is present at the 5' end of all trypanosome mRNAs (the so-called mini-exon sequence). In a rabbit reticulocyte lysate, a nonadeoxynucleotide linked to an acridine derivative, specifically inhibited protein synthesis from T. brucei mRNAs much more efficiently than unmodified oligodeoxynucleotides of similar length. These oligodeoxynucleotides were tested on cultured trypanosomes. The acridine-linked nonadeoxynucleotide had a lethal effect on the parasites. No effect was observed with the homologous unmodified 9-mer nor with those 9-mers linked to the acridine derivative which were not complementary to the mini-exon sequence. These effects are probably a result of hybrid formation between the anti-messenger and mini-exon sequence. Trypanocidal activity of the acridine-modified nonadeoxynucleotide is most likely due to (i) increased affinity for its target, (ii) improved resistance to 3' exonucleases, and (iii) promoted membrane penetration of living parasites.  相似文献   
19.
Strains of Vibrio salmonicida isolated from Atlantic salmon (Salmo salar) and rainbow trout (Salmo gairdneri) suffering from cold-water vibriosis could be divided on the basis of plasmid profiles into four different categories. Of 32 strains, 19% harbored three plasmids of 24, 3.4, and 26 megadaltons (MDa), 69% harbored the 24- and 3.4-MDa plasmids but not the 2.6-MDA plasmid, and 9% harbored only the 24-MDA plasmid. The fourth category, which consisted of only one strain, harbored a plasmid of 10 MDa. In spite of different plasmid patterns, the strains of V. salmonicida were very similar with respect to biochemical reactions. The one-third of the V. salmonicida strains which were serotyped were of the same type. The 50% lethal doses, which were determined by intraperitoneal injection, ranged from 4 x 106 to 1 x 108 CFU per fish.  相似文献   
20.
Tobacco cells are sensitive to bleomycin and phleomycin. The Tn5 and the Streptoalloteichus hindustanus (Sh) bleomycin resistance (Ble) genes conferring resistance to these antibiotics have each been inserted into two plant expression vectors. They are flanked by the nopaline synthase (nos) or the cauliflower mosaic virus (CaMV) 35S promoters on one side, and by the nos polyadenylation signal on the other. These four chimaeric genes were introduced into the binary transformation vector pGA 492, which were thereafter mobilized into Agrobacterium tumefaciens strain LBA 4404. The resulting strains were used to transform Nicotiana tabacum cv. Xanthi nc using the leaf disc transformation procedure. In all cases, phleomycin- and bleomycin-resistant tobacco plants were regenerated from transformed cells under selective conditions; however the highest frequency of rooted plants was obtained when transformation was carried out with the Sh Ble gene under the control of the 35S promoter. Phleomycin resistance was stably transmitted to sexual offspring as a dominant nuclear trait as confirmed by Southern blotting.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号