全文获取类型
收费全文 | 642664篇 |
免费 | 67795篇 |
国内免费 | 419篇 |
专业分类
710878篇 |
出版年
2016年 | 7039篇 |
2015年 | 9477篇 |
2014年 | 11032篇 |
2013年 | 16652篇 |
2012年 | 18011篇 |
2011年 | 18675篇 |
2010年 | 12585篇 |
2009年 | 11637篇 |
2008年 | 16808篇 |
2007年 | 17554篇 |
2006年 | 16608篇 |
2005年 | 15838篇 |
2004年 | 15794篇 |
2003年 | 15423篇 |
2002年 | 15076篇 |
2001年 | 26272篇 |
2000年 | 26366篇 |
1999年 | 21094篇 |
1998年 | 7666篇 |
1997年 | 8197篇 |
1996年 | 7826篇 |
1995年 | 7219篇 |
1994年 | 7060篇 |
1993年 | 7120篇 |
1992年 | 18311篇 |
1991年 | 18124篇 |
1990年 | 17881篇 |
1989年 | 17662篇 |
1988年 | 16476篇 |
1987年 | 15645篇 |
1986年 | 14480篇 |
1985年 | 15090篇 |
1984年 | 12524篇 |
1983年 | 10719篇 |
1982年 | 8344篇 |
1981年 | 7549篇 |
1980年 | 7096篇 |
1979年 | 12049篇 |
1978年 | 9422篇 |
1977年 | 8946篇 |
1976年 | 8439篇 |
1975年 | 9188篇 |
1974年 | 10108篇 |
1973年 | 9940篇 |
1972年 | 9132篇 |
1971年 | 8356篇 |
1970年 | 7333篇 |
1969年 | 7234篇 |
1968年 | 6659篇 |
1967年 | 5779篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
L Brun-Samarcq S Gallina A Philippi F Demenais G Vaysseix E Barillot 《Bioinformatics (Oxford, England)》1999,15(4):345-346
SUMMARY: We developed a collaborative pedigree environment called CoPE. This environment includes a Java program for drawing pedigrees and a standardized system for pedigree storage. Unlike other existing pedigree programs, this software is particularly intended for epidemiologists in the sense that it allows customized automatic drawing of large numbers of pedigrees and remote and distributed consultation of pedigrees. AVAILABILITY: At http://www.infobiogen.fr/services/CoPE 相似文献
992.
F Stephen Perry 《BMJ (Clinical research ed.)》1998,317(7156):481
993.
E B Blanchard M A Gordon D A Wittrock R J McCaffrey G C McCoy V V Khramelashvili 《Biofeedback and self-regulation》1991,16(2):181-190
This study investigated the ability of pretreatment variables from three different domains (social-demographic, psychological, and psychophysiological) to predict posttreatment mean arterial pressure (MAP) for 59 unmedicated males with mild hypertension who were participating in a cross-cultural (USA-USSR) comparison of autogenic training and thermal biofeedback to a self-relaxation control. The overall multiple regression equation consisted of two variables and indicated that higher diastolic blood pressures during a cold pressor task were predictive of greater MAP reductions while higher scores on the Irritability subscale of the Buss-Durkee Hostility Scale were predictive of less MAP reductions. Suggestions for future research in this area are provided. 相似文献
994.
Human umbilical vein endothelial cells were grown to confluence, as first passage cells, on coverslips. Treatment with ionomycin or histamine caused a sustained rise in intracellular Ca2+ (measured by Fura-2 fluorescence), but after treatment with thrombin, only a transient rise in Ca2+ was observed. Furthermore, the addition of thrombin after ionomycin or histamine lowered the raised Ca2+ back to near control levels. This effect of thrombin was concentration dependent, with increasing concentrations producing increases in both the rate and extent of the lowering of Ca2+. A similar effect of thrombin was seen on video imaging of Fura-2-loaded cell monolayers. The Ca2(+)-lowering effect of thrombin was not mimicked by phorbol 12-myristate 13-acetate nor blocked by staurosporine, indicating a lack of involvement of protein kinase C; intracellular pH also does not appear to be involved. The mechanism by which thrombin lowers cytoplasmic Ca2+ is due mainly to inhibition of Ca2+ entry since thrombin prevented the stimulated influx of Mn2+ caused by histamine or ionomycin. It may therefore be that in vivo under certain physiological or pathological conditions, thrombin's effects on intracellular Ca2+ are more transient than those of histamine, and thrombin also may induce transience in histamine's actions. 相似文献
995.
An eight-nucleotide sequence in the potato virus X 3' untranslated region is required for both host protein binding and viral multiplication. 总被引:3,自引:1,他引:2 下载免费PDF全文
Gel retardation and UV-cross-linking techniques were used to demonstrate that two tobacco proteins, with approximate molecular masses of 28 and 32 kDa, bind to a site within the 3' region of potato virus X (PVX) genomic RNA. The protein binding is specific, in that a 50-fold excess of unlabeled probe prevents formation of the complexes but no reduction is observed with a 2,000-fold molar excess of yeast tRNA. Complex formation is inhibited by poly(U) but is relatively unaffected by poly(A), poly(G), or poly(C-I). PVX RNA-host protein complex formation occurs in vitro at salt concentrations up to 400 mM. Deletion mapping indicates that the proteins bind within the 3' untranslated region (UTR) of PVX genomic RNA and that an 8-nucleotide U-rich sequence (5'-UAUUUUCU) is required for the binding. Deletion of the 8-nucleotide U-rich region from the 3' UTR of a sensitive PVX reporter virus that carries the luciferase gene in place of the PVX coat protein gene results in a more than 70,000-fold reduction in luciferase expression in tobacco protoplasts. RNA probes carrying the sequence GCGC in place of the central four contiguous uridines of the 8-nucleotide U-rich motif fail to bind host protein at detectable levels, and the same mutation, when introduced into the PVX reporter virus, eliminates viral multiplication. Mutations of 1 or 2 nucleotides within the same four uridines reduced both binding of host proteins and replication of reporter virus. These results indicate that the 8-nucleotide U-rich motif within the PVX 3' UTR is important for some aspect of viral multiplication and suggest that host protein binding plays a role in the process. 相似文献
996.
The involvement of gibberellins in the control of flowering of sunflower was studied by direct application of GA3 to the apex of the plants, analysis of the endogenous levels of gibberellin-like substances at different plant ages, and indirectly by the application of paclobutrazol, an inhibitor of gibberellin synthesis. GA3 speeded-up flower initiation and floral apex development. The time of GA3 application was more critical than the amount of GA3 applied. The endogenous levels of gibberellin-like compounds increased significantly by day 15 after sowing. The application of paclobutrazol markedly delayed floral initiation and this effect was also depedent on plant age. Both GA3 and paclobutrazol had their greatest effects between 10 and 20 days after sowing suggesting that an increase in gibberellins in that time period plays a role in floral initiation. 相似文献
997.
998.
Preventing the establishment of ectoparasitic poultry red mite (Dermanyssus gallinae) populations is key in ensuring welfare and egg production of laying hens and absence of allergic reactions of workers in poultry facilities. Using the Hazard Analysis and Critical Control Point method, a panel of experts identified hazards and associated risks concerning the introduction and spread of this mite in poultry facilities. Together we provide an overview of possible corrective actions that can be taken to prevent population establishment. Additionally, a checklist of the most critical control points has been devised as management tool for poultry farmers. This list was evaluated by Dutch and British poultry farmers. They found the checklist feasible and useful. 相似文献
999.
1000.