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   332999篇
  免费   37178篇
  国内免费   190篇
  370367篇
  2018年   2838篇
  2017年   2698篇
  2016年   3870篇
  2015年   5328篇
  2014年   6230篇
  2013年   8751篇
  2012年   9981篇
  2011年   9956篇
  2010年   6804篇
  2009年   6146篇
  2008年   8854篇
  2007年   9301篇
  2006年   8591篇
  2005年   8282篇
  2004年   8004篇
  2003年   7757篇
  2002年   7764篇
  2001年   18142篇
  2000年   18373篇
  1999年   14101篇
  1998年   4228篇
  1997年   4503篇
  1996年   4302篇
  1995年   4011篇
  1994年   3947篇
  1993年   3787篇
  1992年   11480篇
  1991年   11125篇
  1990年   10677篇
  1989年   10247篇
  1988年   9486篇
  1987年   8840篇
  1986年   8079篇
  1985年   7960篇
  1984年   6391篇
  1983年   5566篇
  1982年   4107篇
  1981年   3595篇
  1980年   3354篇
  1979年   6116篇
  1978年   4575篇
  1977年   4126篇
  1976年   3763篇
  1975年   4332篇
  1974年   4498篇
  1973年   4395篇
  1972年   4099篇
  1971年   3512篇
  1970年   3169篇
  1969年   2974篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The level of urine selenium in healthy adult population, 230 persons, was examined. Persons were selected regarding sex, ages, and smoking habits. No differences versus these observations have been found. For a total, group values are 16.96 Se nmol/creatinine mmol, SD=5.44. It is possible from a single-void specimen to express daily excretion of selenium.  相似文献   
993.
Administration of high-dose Antide to ovariectomized monkeys results in rapid, prolonged, and reversible inhibition of gonadotropin secretion. The present study examined whether similar long-term control would be manifested in the menstrual cycle of intact primates. Antide administration at a dose of either 3.0 or 18.0 mg/kg induced rapid suppression of bioassayable LH concentrations, precipitating a concurrent fall in serum progesterone concentrations from 7.9 +/- 3.6 and 5.8 +/- 1.0 ng/ml (mean +/- SEM) on the day of injection to 0.6 +/- 0.2 and 0.5 +/- 0.1 ng/ml by 2 days post-treatment, respectively. This Antide-induced luteolysis was accompanied by the premature onset of menses within 3 days. The next menses following Antide administration was delayed. Ultimately, folliculogenesis culminating in normal follicular-phase estradiol production, ovulation, and subsequent normal luteal-phase progesterone production did occur in all treated monkeys. Menses resumed 54 +/- 9 and 75 +/- 13 days after treatment with 3.0 and 18.0 mg/kg Antide, respectively. No allergic cutaneous or peripheral reactions were seen, even at the highest dose of Antide. Thus, the long duration of action of high-dose Antide reported earlier in ovariectomized monkeys is also demonstrated in intact primates. These findings, along with the apparent absence of histamine-release effects even at high doses, suggest that Antide is a GnRH antagonist deserving clinical evaluation.  相似文献   
994.
995.
996.
997.
998.
Restriction fragment length polymorphisms (RFLPs) were described for the porcine loci for β-glucosidase (GBA) and the β-polypeptide 1 of the Na+, K+-transporting ATPase (ATP1B1). Linkage analyses using a three-generation pedigree provided evidence for the assignment of ATP1B1, GBA and two microsatellite loci (S0001 and S0067) to a previously described linkage group comprising the loci for blood group L (EAL) and an anonymous microsatellite (S0097). The linear order of the six markers was determined with confidence by multipoint analyses and the length of the linkage group was estimated at 88 CM. This linkage group was assigned to pig chromosome 4 on the basis of a previous physical localization of the ATP1B1 gene. In situ hybridization data for S0001 presented in this study were consistent with a localization on chromosome 4 and suggested a regional localization to 4pl2-pl3. The present study reveals conflicting data concerning the genetic localization of the K88 loci controlling the expression of the receptors for the E. coli pilus antigens. One group has reported data suggesting a loose linkage between K88 and EAL, now mapped to chromosome 4, whereas two other groups have found linkage between K88 and the transferrin locus (TF), mapped to chromosome 13 by in situ hybridization.  相似文献   
999.
Abstract Monoclonal antibodies have been developed and used as specific probe to locate and identify a 29-kDa molecule of axenic Entamoeba histolytica trophozoites. Monoclonal antibody produced by clone C8 (MoAb C8) strongly agglutinated the amoebic trophozoites. THe immunofluorescence of live E. histolytica trophozoites and surface fluorescence of acetone-fixed trophozoites by MoAb C8 indicated existence of a 29-kDa molecule on surface-associated plasma membrane of E. histolytica . The monoclonal antibody belonged to IgG1 isotype. The prior treatment of E. histolytica trophozoites with MoAb C8 resulted in significant ( P < 0.01) reduction in adherence of amoebic trophozoites to cultured Chinese Hamster Ovary cells and significant ( P < 0.01) reduction in cytotoxicity to cultured Baby Hamster Kidney cells. Pretreatment of amoebic trophozoites with MoAb C8 prior to cultivation in TPS-1 medium resulted in significant ( P < 0.01) reduction in growth of the parasite. Thus, the data suggested that the surface-exposed 29-kDa molecule may be one of the receptors involved in E. histolytica host cell interactions and may possibly modulate amoebic disease processes.  相似文献   
1000.
Based on quantitative measurement of components of field resistance of potatoes to late blight, a multiple linear regression equation is derived for laboratory estimation of Area Under Disease Progress Curve. The equation accounts for 82% of variation in Area Under Disease Progress Curve. Transformation of data or inclusion of more terms do not improve the equation significantly. The method is suggested as a replacement or supplement to field testing.  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