全文获取类型
收费全文 | 90022篇 |
免费 | 3868篇 |
国内免费 | 3561篇 |
出版年
2023年 | 746篇 |
2022年 | 997篇 |
2021年 | 2417篇 |
2020年 | 1606篇 |
2019年 | 2156篇 |
2018年 | 1852篇 |
2017年 | 1401篇 |
2016年 | 2014篇 |
2015年 | 3925篇 |
2014年 | 7526篇 |
2013年 | 7554篇 |
2012年 | 5514篇 |
2011年 | 6587篇 |
2010年 | 4686篇 |
2009年 | 4558篇 |
2008年 | 4650篇 |
2007年 | 4961篇 |
2006年 | 3582篇 |
2005年 | 3152篇 |
2004年 | 2277篇 |
2003年 | 2072篇 |
2002年 | 1820篇 |
2001年 | 1335篇 |
2000年 | 1196篇 |
1999年 | 1131篇 |
1998年 | 969篇 |
1997年 | 768篇 |
1996年 | 822篇 |
1995年 | 1036篇 |
1994年 | 922篇 |
1993年 | 879篇 |
1992年 | 842篇 |
1991年 | 763篇 |
1990年 | 631篇 |
1989年 | 604篇 |
1988年 | 584篇 |
1987年 | 516篇 |
1986年 | 459篇 |
1985年 | 742篇 |
1984年 | 1049篇 |
1983年 | 688篇 |
1982年 | 908篇 |
1981年 | 880篇 |
1980年 | 654篇 |
1979年 | 619篇 |
1978年 | 405篇 |
1977年 | 423篇 |
1976年 | 381篇 |
1974年 | 268篇 |
1973年 | 273篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Whole cells of Chlorella vulgaris and Clostridium butyricum were co-immobilized in 2% agar gel. NADP was suitable as an electron carrier. The rate of hydrogen evolution increased with increasing NADP concentration. The optimum conditions for hydrogen evolution were pH 7.0 and 37°C. The immobilized C. vulgaris-NADP-immobilized Cl. butyricum system continuously evolved hydrogen at a rate of 0.29–1.34 μmol/h per mg Chl for 6 days. On the other hand, the system without NADP evolved only a trace amount of hydrogen. 相似文献
993.
Bernd Höffken Reinhard Ködding Alexander von zur Mühlen Tainer Hehrmann Rolf-Dieter Hesch 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(1):114-124
The nature of the conversion of thyroxine (T4) to triiodothyronine (T3) and reverse triiodothyronine (rT3) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T3 and 2.5-fold rise of rT3 levels determined by specific radioimmunoassays was observed over 6 h after the addition of T4. An enzymic process is suggested that converts T4 to T3 and rT3. For T3 the optimal pH is 6 and for rT3, 9.5. The converting activity for both T3 and rT3 is temperature dependent and can be suppressed by heat, H2O2, merthiolate and by 5-propyl-2-thiouracil. rT3 and to a lesser degree iodide, were able to inhibit the production of T3 in a dose related fashion. Therefore the pH dependendy, rT3 and iodide may regulate the availability of T3 or rT3 depending on the metabolic requirements of thyroid hormones. 相似文献
994.
995.
T.G. Adelman P. Arosio J.W. Drysdale 《Biochemical and biophysical research communications》1975,63(4):1056-1062
The subunit composition of human heart and liver ferritins was examined by both sodium dodecyl sulfate gel electrophoresis and acetic acidurea gel electrophoresis. These analyses indicated that both tissues contained two subunit types of similar size but different surface charge. One subunit was common to both tissues. The implications of these findings in relation to the known heterogeneity of isoferritins are discussed, and a new model of ferritin structure is proposed. 相似文献
996.
Jan Dirk van Elsas Alexander V Semenov Rodrigo Costa Jack T Trevors 《The ISME journal》2011,5(2):367-183
In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health. 相似文献
997.
998.
999.
Beatriz Llano-Sotelo 《Journal of molecular biology》2009,391(5):813-9353
Identification of small molecular weight compounds targeting specific sites in the ribosome can accelerate development of new antibiotics and provide new tools for ribosomal research. We demonstrate here that antibiotic-size short peptides capable of inhibiting protein synthesis can be selected by using specific elements of ribosomal RNA as a target. The ‘h18’ pseudoknot encompassing residues 500-545 of the small ribosomal subunit RNA was used as a target in screening a heptapeptide phage-display library. Two of the selected peptides could efficiently interfere with both bacterial and eukaryotic translation. One of these inhibitory peptides exhibited a high-affinity binding to the isolated small ribosomal subunit (Kd of 1.1 μM). Identification of inhibitory peptides that likely target a specific rRNA structure may pave new ways for validating new antibiotic sites in the ribosome. The selected peptides can be used as a tool in search of novel site-specific inhibitors of translation. 相似文献
1000.
Caveolin-1 (Cav-1) plays an important role in the organization of signaling molecules involved in a variety of signaling pathways, including those mediating cell motility. Here we show that amino acids K47-K57 of Cav-1 are a highly conserved sequence in Cav-1 and Cav-3 proteins, and that expression of either K47-K57 deletion Cav-1 mutant or wild-type Cav-2 that lacks this sequence exhibits a non-polarized distribution pattern. Expression of K47-K57 in Cav-2 leads to Cav-2 polarity, suggesting that expression of K47-K57 is sufficient to direct caveolin polarity. Importantly, we show that expression of this sequence is both necessary and sufficient to promote cell directional migration. Thus, our results support the conclusion that Cav-1 polarity is critical for cell directional migration. 相似文献