全文获取类型
收费全文 | 4532篇 |
免费 | 327篇 |
专业分类
4859篇 |
出版年
2023年 | 26篇 |
2022年 | 67篇 |
2021年 | 128篇 |
2020年 | 79篇 |
2019年 | 96篇 |
2018年 | 132篇 |
2017年 | 107篇 |
2016年 | 175篇 |
2015年 | 254篇 |
2014年 | 265篇 |
2013年 | 368篇 |
2012年 | 407篇 |
2011年 | 388篇 |
2010年 | 236篇 |
2009年 | 234篇 |
2008年 | 301篇 |
2007年 | 252篇 |
2006年 | 216篇 |
2005年 | 224篇 |
2004年 | 203篇 |
2003年 | 184篇 |
2002年 | 145篇 |
2001年 | 28篇 |
2000年 | 16篇 |
1999年 | 24篇 |
1998年 | 23篇 |
1997年 | 28篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有4859条查询结果,搜索用时 0 毫秒
991.
We measured the chemiluminescence (CL) of human neutrophils (PMNLs) exposed to different concentrations of ofloxacin (2, 4, and 6 μg/ml) readily achievable in therapy. CL reaction during zymosan phagocytosis by PMNLs obtained from human healthy volunteers was registered in a computer-linked LKB 1251 luminometer. Ofloxacin did not induce significant variations on the respiratory burst of PMNLs. 相似文献
992.
993.
Hypersensitive confluent necrosis in tobacco leaves, caused by Pseudomonas syringae pv. aptata, is prevented by an intercellular injection of protein-lipopolysaccharide (pr-LPS) complexes 48 h earlier. An increase (48 %) in the peroxidase activity and a new low molecular weight protein (ε 17.5 kD) were found in the intercellular fluid of protected tissue (treated fluid) 48 h after pr-LPS infiltration. Up to 24 h after pr-LPS infiltration the treated fluid did not inhibit the in vitro growth of heterologous bacteria. Injected into tobacco leaves 30 min before the bacteria, the treated fluid retarded the rate of intercellular bacterial growth between 8 and 12 h after infiltration of the bacteria compared with the control fluid. Up to 4 h after injection, the attachment of live and dead bacteria to the cell walls occurred in both the protected tissue and in the control; 4 h after injection, however, the dead bacteria were only weakly attached in the protected tissue. Within 20 min after the intercellular infiltration, there was a decrease in the heterologous bacterial number in the protected tissue, 33 % less than that in the control tissue. Protected tissue free-space solutes did not have a direct antibacterial effect but activated an antibacterial response in the leaf tissue. Attachment of bacteria to the cell walls did not in itself trigger hypersensitive confluent necrosis. The protected tissue was initially more favourable for the survival of heterologous bacteria. 相似文献
994.
Suzuki Hisanori Buonamassa Daniela Tornese Weisz Alessandro 《Molecular and cellular biochemistry》1990,99(1):33-39
Summary The activity of poly (ADP-ribose) polymerase (ADPRP) and the content of 2,5-oligodenylates core (2,5An; n = 2,3 and 4) were measured in homogenates of the uterus and of the liver of immature rats immediately before (time 0) or at different times after injection of estradiol-valerate. ADPRP activity increased gradualy, starting 6 hours after estrogen injection, for about 4 days. Instead, the content of 2,5 An decreased by about 50% within 6 hours, and thereafter more slowly for 4 days to about 20% of starting values. Estrogen increased ADPRP activity and decreased 2,5An concentration also in the kidney and in the cardiac muscle of the same animals, but not in the skeletal muscle, where neither of the two parameters was affected. Injection of vehicle only (sesame oil) had no effect on ADPRP activity nor on 2,5An content of immature rat tissues. 相似文献
995.
Deoxyribonucleic Acid Base Composition of Species in the Yeast Genus Kluyveromyces van der Walt emend. van der Walt 总被引:1,自引:0,他引:1 下载免费PDF全文
The deoxyribonucleic acid base composition (percent guanine + cytosine [GC]) was determined for 29 strains, representing 18 species of the genus Kluyveromyces. It was concluded that on the basis of GC content (47.4%) and other properties K. veronae occupies an uncertain position in the genus Kluyveromyces. The GC content of the remaining 17 species ranged from 35.3 to 43.4%, and three groups of species were recognized. The GC content of the first ranged from 35.3 to 38.0%; that of the second group from 39.5 to 41.7%; that of the third group from 42.4 to 43.4%. Several species revealed a nearly identical GC content. The GC contents do not correspond in all instances with the five groups of species proposed by van der Walt. 相似文献
996.
Harry A. Kuiper Lello Zolla Alessandro Finazzi-Agró Maurizio Brunori 《Journal of molecular biology》1981,149(4):805-812
The interaction of a number of lanthanide ions (namely terbium, praseodymium, erbium, lanthanum, gadolinium and europium) with Panulirus interruptus hemocyanin has been studied.Results from O2-binding experiments indicate that all these ions may substitute for calcium as allosteric effectors of hemocyanin. Addition of the lanthanides to deoxygenated Panulirus hemocyanin saturated with Tb3+ results in a quenching of the terbium luminescence. The highly efficient quenching observed in the case of Eu3+ may indicate energy-transfer between Tb3+ and Eu3+. Since energy-transfer between lanthanides is only effective over very short distances, the data suggest that some of the cation binding sites of Panulirus hemocyanin are clustered. 相似文献
997.
Inhibition by ricin of protein synthesis in vitro: 60S ribosomal subunit as the target of the toxin (Short Communication) 总被引:1,自引:0,他引:1
Simonetta Sperti Lucio Montanaro Alessandro Mattioli Fiorenzo Stirpe 《The Biochemical journal》1973,136(3):813-815
Poly(U)-directed polyphenylalanine synthesis by rat liver ribosomes is strongly inhibited by ricin. Experiments involving hybridization between subunits derived from normal and ricin-treated ribosomes demonstrate that the 60S subunit is the site of action of the toxin. The toxin inactivates the 60S subunit independently of the presence of the 40S subunit. 相似文献
998.
Increase of rooting ability in the woody species kiwi (Actinidia deliciosa A. Chev.) by transformation with Agrobacterium rhizogenes rol genes 总被引:1,自引:0,他引:1
Eddo Rugini Alessandro Pellegrineschi Massimo Mencuccini Domenico Mariotti 《Plant cell reports》1991,10(6-7):291-295
Summary The woody species kiwi (Actinidia deliciosa A. Chev.), a male and late flowering clone of the cv Hayward, has been transformed by a T-DNA fragment encompassing rol A, B, C genes of A. rhizogenes. Transgenic plants, regenerated from leaf disc callus, showed the typical hairy root phenotype as described in herbaceous species. Explants from these plants (both leaf discs or 3 to 4 node leafy microcuttings) showed an increased ability to produce roots. Since root formation is one of the limiting factors in the vegetative propagation of woody species, the results have been discussed in relation to the use of A. rhizogenes rol genes in improving root morphogenesis in trees. 相似文献
999.
Pirelli A Allavena P Rambaldi A Di Bello M Pirovano P Peccatori F Mantovani A 《Cytotechnology》1987,1(1):79-81
The lineage to which normal large granular lymphocytes/natural killer (LGL/NK) cells belong is controversial; in fact they share some surface markers and functional activities with monocytes, but also with T lymphocytes. The relationship of LGL to the T cell lineage by analysis with the T cell receptor (T-rec) gene has been investigated. Pure preparations of human LGL and their CD11+ CD8- and CD11- CD8+ subsets had the T gene in its unrearranged germline configuration. Expression of T and T genes was not detectable. The organization of T gene, which is of particular importance because it occurs early in T cell ontogeny, was also found in its germline configuration.A rare type of lymphoproliferative disorder, termed T-LPD, is characterized by expansion of cells very similar to LGL for morphology, phenotype, and functional activity. Of 17 patients with T-LPD studied for T-rec rearrangement, 15 displayed rearrangement of T and T loci and were CD3+ (14/15 had monoclonal rearrangement), while 2 cases were in germline configuration and were CD3–. Similarly to very small subsets of CD3+ LGL recently described, most T-LPD cases are CD3+ and have T-rec genes rearranged. These data suggest that either a subset of LGL or a particular step of differentiation may be related to the T cell lineage; they also demonstrate that, in contrast to previous views, most TLPD are monoclonal, presumably neoplastic, lymphoproliferative disorders.Abbreviations LGL
large granular lymphocytes
- NK
natural killer
- T-rec
T-cell receptor
- TLPD
T lymphoproliferative disease 相似文献
1000.
Araya E Rodriguez A Rubio J Spada A Joglar J Llebaria A Lagunas C Fernandez AG Spisani S Perez JJ 《Bioorganic & medicinal chemistry letters》2005,15(5):1493-1496
Peptide T (ASTTTNYT) is a promising molecule to prevent the neuropsychometric symptoms of patients suffering AIDS and for the treatment of psoriasis. In order to fully prove its therapeutic benefits, efforts were put forward to design peptidomimetics of the peptide. In this direction, in a recent computational study the natural product amygdalin was identified as a prospective peptidomimetic of the peptide and later proved to exhibit a similar chemotactic profile to the peptide. However, the cyanide moiety of amygdalin provides to the molecule a toxic profile. The present study reports the synthesis of a set of amygdalin analogs lacking the cyanide group with improved chemotactic profiles. 相似文献