全文获取类型
收费全文 | 41821篇 |
免费 | 3708篇 |
国内免费 | 205篇 |
专业分类
45734篇 |
出版年
2018年 | 494篇 |
2017年 | 480篇 |
2016年 | 623篇 |
2015年 | 701篇 |
2014年 | 902篇 |
2013年 | 1073篇 |
2012年 | 1221篇 |
2011年 | 1259篇 |
2010年 | 851篇 |
2009年 | 863篇 |
2008年 | 1176篇 |
2007年 | 1168篇 |
2006年 | 1179篇 |
2005年 | 1002篇 |
2004年 | 965篇 |
2003年 | 910篇 |
2002年 | 888篇 |
2001年 | 2776篇 |
2000年 | 2456篇 |
1999年 | 1799篇 |
1998年 | 612篇 |
1997年 | 525篇 |
1996年 | 470篇 |
1995年 | 400篇 |
1994年 | 386篇 |
1992年 | 1280篇 |
1991年 | 1158篇 |
1990年 | 1095篇 |
1989年 | 1043篇 |
1988年 | 928篇 |
1987年 | 922篇 |
1986年 | 803篇 |
1985年 | 793篇 |
1984年 | 563篇 |
1983年 | 513篇 |
1982年 | 366篇 |
1979年 | 631篇 |
1978年 | 451篇 |
1977年 | 416篇 |
1976年 | 368篇 |
1975年 | 494篇 |
1974年 | 575篇 |
1973年 | 553篇 |
1972年 | 572篇 |
1971年 | 548篇 |
1970年 | 520篇 |
1969年 | 526篇 |
1968年 | 426篇 |
1967年 | 373篇 |
1966年 | 409篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
A total of 626 patients undergoing a prostaglandin-induced abortion, the majority in the second trimester, have been analysed for complications occurring during inpatient treatment. Of the last 155 consecutive patients 143 were critically assessed six to eight weeks after abortion for morbidity occurring during their early recovery period.Blood loss of 250 ml or more occurred in 68 patients, pyrexia in 34, pelvic infection in three, and readmission in 14 of the 626 patients studied, and a transfusion was required in eight.Bleeding after abortion stopped within six weeks in all 143 of the 155 consecutive patients assessed but three required readmission for uterine curettage. Menstruation was re-established within six weeks of abortion in 106 patients.The incidence of operative morbidity was similar to that reported for first trimester abortion and better than that in most reported series of second trimester abortions. 相似文献
103.
104.
105.
106.
107.
WIKTOR Z 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1952,7(27-28):908-915
108.
Affinity labeling studies of NADP(+)-glutamate dehydrogenase from Salmonella typhimurium have shown that the peptide Leu-282-Lys-286 is located near the coenzyme site [Haeffner-Gormley et al. (1991) J. Biol. Chem. 266, 5388-5394]. The present study was undertaken to evaluate the role of lysine-286. The mutant enzymes K286R, K286Q, and K286E were prepared by site-directed mutagenesis, expressed in Escherichia coli, and purified. The Vmax values (micromoles of NADPH per minute per milligram of protein) were similar for WT (270), K286R (529), K296Q (409), and K286E (382) enzymes. As measured at pH 7.9, the Km value for NADPH was much greater for K286E (280 microM) than for WT (9.8 microM), K286R (30 microM), or K286Q (66 microM) enzymes. The efficiencies (kcat/Km) of the WT and K286R mutant were similar (1.2 x 10(3) min-1 microM-1 and 1.0 x 10(3) min-1 microM-1, respectively) while those of K286Q (0.30 x 10(3) min-1 microM-1) and K286E (0.07 x 10(3) min-1 microM-1) were greatly reduced. The decreased efficiency of the K286E mutant results from the increase in Km-NADPH, consistent with a role for a basic residue at position 286 which enhances the binding of NADPH. Plots of Vmax vs pH showed the pH optima to be 8.1-8.3 for all enzymes at saturating NADPH concentrations. A 40-fold increase in Km-NADPH for K286E was observed as the pH increased from 5.98 to 8.08, from which a unique pKe of 6.5 was calculated.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
109.
S A Bitko L O Dynga A R Shikhman Z F Shmakova N I Briko 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1990,(4):3-7
The amino acid composition of cell walls and surface proteins, isolated from virulent (M+) and avirulent (M-) streptococcal strains (group A, type 29) has been determined by the method of E. H. Beachey et al. The kinetics of the lysis and proteolysis of streptococcal cell walls with muramidase and protease obtained from Actinomyces levoris and streptolysin has been studied. The constants describing the progress rates of these processes has been determined; their values in case of both lysis and proteolysis are higher in virulent strains than in avirulent ones. 相似文献
110.
Z Naor 《Biochemical and biophysical research communications》1990,167(3):982-992
Addition of the stable and permeable analog 8-bromo cyclic GMP (8-BR-cGMP) to myo-[2-3H]inositol prelabeled cultured rat pituitary cells results in enhanced formation of [3H]-myo-inositol monophosphate (IP1). The stimulatory effect of the cyclic nucleotide analog is additive to the effect of Li+, which accumulates IP1 via inhibition of inositol 1-monophosphatase, and also to the effect of gonadotropin releasing hormone (GnRH) which stimulates the formation of IP1, as well as that of inositol 1,4-bisphosphate (IP2) and inositol 1,4,5-trisphosphate (IP3) via enhanced hydrolysis of polyphosphoinositides. Many Ca2(+)-mobilizing hormones acting via phosphoinosite turnover also stimulate cGMP formation. The cyclic nucleotide might then serve as a modulator by further hydrolysis of phosphoinositides needed for protein kinase C activation. 相似文献