全文获取类型
收费全文 | 3705篇 |
免费 | 243篇 |
国内免费 | 205篇 |
出版年
2023年 | 55篇 |
2022年 | 85篇 |
2021年 | 107篇 |
2020年 | 107篇 |
2019年 | 138篇 |
2018年 | 125篇 |
2017年 | 80篇 |
2016年 | 114篇 |
2015年 | 121篇 |
2014年 | 198篇 |
2013年 | 266篇 |
2012年 | 165篇 |
2011年 | 232篇 |
2010年 | 171篇 |
2009年 | 210篇 |
2008年 | 233篇 |
2007年 | 229篇 |
2006年 | 173篇 |
2005年 | 151篇 |
2004年 | 130篇 |
2003年 | 128篇 |
2002年 | 107篇 |
2001年 | 46篇 |
2000年 | 54篇 |
1999年 | 47篇 |
1998年 | 45篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1986年 | 4篇 |
1985年 | 27篇 |
1984年 | 41篇 |
1983年 | 54篇 |
1982年 | 50篇 |
1981年 | 38篇 |
1980年 | 36篇 |
1979年 | 32篇 |
1978年 | 34篇 |
1977年 | 36篇 |
1976年 | 26篇 |
1975年 | 22篇 |
1974年 | 19篇 |
1973年 | 10篇 |
排序方式: 共有4153条查询结果,搜索用时 15 毫秒
61.
Under the protection of ascorbic acid a 2-hydroxyestrone bovine serum albumin conjugate was prepared containing intact 2-hydroxyestrone as determined by gas chromatographymass spectrometry. Using this antigen highly specific antibodies were raised in rabbits. Cross-reactivity for 2-hydroxyestradiol and 2-hydroxyestriol was 26 and 4.5%, respectively. An assay procedure of 2-hydroxyestrone in human plasma is described. Using special precautions the assay allows the determination of 2-hydroxyestrone in plasma samples of women (50–95 pg/ml), pregnant women (105–220 pg/ml), men (45–65 pg/ml) and children (20–40 pg/ml). 相似文献
62.
Arpad I. Csapo 《Prostaglandins & other lipid mediators》1977,13(5):965-973
Following ovariectomy of five New Zealand white rabbits at day 25 of pregnancy, the intrauterine pressure (IUP) and uterine progesterone (P) and prostaglandin (PG) levels were measured sequentially at days 25, 26 and 27. At day 25, when the uterine P and PGE and PGF were high, massive intrauterine treatment with 500 μg PGF2α provoked only a sustained contracture on which only low level oscillation in IUP was superimposed. At day 26, when the P levels had decreased significantly (P<0.001) and the PG levels had not changed significantly, 50 μg PGF2α significantly increased cyclic IUP as compared with the day 25 value (P<0.001). At day 27, when the P levels decreased further, as little as 5 μg PGF2α provoked still higher cyclic IUP, in spite of a significant reduction in PG levels (P<0.05).Stretching the uterus of six post partum and six 26 days pregnant rabbits (after removing the uterine contents) significantly increased the uterine PGF levels (P<0.001). However, stretch increased only cyclic IUP of the post partum uterus and was without effect on the pregnant uterus, which still had high P levels. These results indicate that the myometrium
activated by exogenous PG or stretch, regardless of whether the uterine PG levels increase, remain unchanged or even moderately decrease, provided that the uterine P levels are reduced to a critical value. 相似文献
63.
The extracellular chitinase produced by Serratia marcescens was obtained in highly purified form by adsorption-digestion on chitin. After gel electrophoresis in a nondenaturing system, the purified preparation exhibited two major protein bands that coincided with enzymatic activity. A study of the enzyme properties showed its suitability for the analysis of chitin. Thus, the chitinase exhibited excellent stability, a wide pH optimum, and linear kinetics over a much greater range than similar enzymes from other sources. The major product of chitin hydrolysis was chitobiose, which was slowly converted into free N-acetylglucosamine by traces of β-N-acetylglucosaminidase present in the purified preparation. The preparation was free from other polysaccharide hydrolases. Experiments with radiolabeled yeast cell walls showed that the chitinase was able to degrade wall chitin completely and specifically. 相似文献
64.
Mikael Esmann 《生物化学与生物物理学报:生物膜》1982,688(1):260-270
1. Modification of the Class II sulphydryl groups on the (Na+ + K+)-ATPase from rectal glands of Squalus acanthias with N-ethylmaleimide has been used to detect conformational changes in the protein. The rates of inactivation of the enzyme and the incorporation of N-ethylmaleimide depend on the ligands present in the incubation medium. With 150 mM K+ the rate of inactivation is largest (k1 = 1.73 mM?1 · min?1) and four SH groups per α-subunit are modified. The rate of inactivation in the presence of 150 mM Na+ is smaller (k1 = 1.08 mM?1 · min-1) but the incorporation of N-ethylmaleimide is the same as with K+. 2. ATP in micromolar concentrations protects the Class II groups in the presence of Na+ (k1 = 0.08 mM?1 · min?1 at saturating ATP) and the incorporation id drastically reduced. ATP in millimolar concentrations protects the Class II groups partially in the presence of K+ (k1 = 1.08 mM?1 · min?1) and three SH groups are labelled per α subunit. 3. The K+ -dependent phosphatase is inhibited in parallel to the (Na+ + K+)-ATPase under all conditions, and the ligand-dependent incorporation of N-ethylmaleimide was on the α-subunit only. 4. It is shown that the difference between the Na+ and K+ conformations sensed with N-ethylmaleimide depends on the pH of the incubation medium. At pH 6 there is a very small difference between the rates of inactivation in the presence of Na+ and K+, but at higher pH the difference increases. It is also shown that the rate of inactivation has a minimum at pH 6.9, which suggests that the conformation of the enzyme changes with pH. 5. Modification of the Class III groups with N-ethylmaleimide-whereby the enzyme activity is reduced from about 16% to zero-shows that these groups are also sensitive to conformational changes. As with the Class II groups, ATP in micromolar concentrations protects in the presence of Na+ relative to Na+ or K+ alone. ATP in millimolar concentrations with K+ present increases the rate of inactivation relative to K+ alone, in contrast to the effect on the Class II groups. 6. Modification of the Class II groups with a maleimide spin label shows a difference between Class II groups labelled in the presence of Na+ (or K+) and Class II groups labelled in the presence of K + ATP, in agreement with the difference in incorporation of N-ethylmaleimide. The spectra suggest that the SH group protected by ATP in the presence of K+ is buried in the protein. 7. The results suggest that at least four different conformations of the (Na+ + K+)-ATPase can be sensed with N-ethylmaleimide: (i) a Na+ form of the enzyme with ATP bound to a high-affinity site (E1-Na-ATP); (ii) a Na+ form without ATP bound (E1-Na); (iii) a K+ form without ATP bound (E2-K); and (iv) an enzyme form with ATP bound to a low-affinity site in the presence of K+, probably and E1-K-ATP form. 相似文献
65.
G Vollmer A Haase K Eisele 《Biochemical and biophysical research communications》1982,105(4):1554-1560
Examination of binding of androgen-receptor complexes from murine skeletal muscle cytosol was performed by modified nuclear retention assay and modified nuclear acceptor assay. The experiments showed the binding of androgen-receptor complexes to the nuclear acceptor sites to be a cooperative process. Hill analysis of the data obtained resulted in a Hill coefficient of 3,6. The apparent dissociation constant for binding of cytosolic [3H]-testosterone-receptor complexes to nuclei was found to be in the range of KD = 6 ? 8 × 10?11 M. The nuclear matrix was able to bind androgen-receptor complexes in a saturable way, too. 相似文献
66.
A D-2 dopamine receptor and a β2-adrenoceptor occur in the intermediate lobe of the rat pituitary gland (IL). Exposure of intact IL tissue to a D-2 agonist diminished the ability of dopaminergic agonists [but not 5′-guanylyl imidodiphosphate (Gpp(NH)p)] to inhibit adenylate cyclase activity. Conversely, exposure of intact IL tissue to a β-adrenergic agonist diminished the ability of a β-adrenergic agonist (but not forskolin) to stimulate adenylate cyclase activity. Treatment of ovariectomized rats with 17β-estradiol desensitizes the β2-adrenoceptor but not the D-2 receptor. Desensitization of the IL catecholamine receptors is discussed within the framework of a previously published “working model” of these receptors. 相似文献
67.
The nonelectrophoretic transfer of proteins from thin (0.5 mm) isoelectric focusing gels to nitrocellulose was complete in 1 h. Blotting was bidirectional with 60% of the protein transferred to the top blot and the remaining 40% to the bottom blot. The use of nondenaturing transfer buffers permits proteins to be blotted in the native state. Immunological determinants are preserved and enzyme activity can be detected on the blots. 相似文献
68.
Michael Bulmer 《Journal of molecular evolution》1991,33(4):305-310
Summary It has been suggested that there may be inequalities in the types of substitution on the two DNA strands (in particular, in the frequencies of transversions from R to Y and from Y to R) due to a higher error rate on the lagging than the leading strand during replication. Reexamination of 11 kb of the -globin region sequenced in six primates fails to confirm this suggestion. Examination of the 73-kb -globin region sequenced in humans shows that the frequency of pyrimidines in different parts of this region is more variable than expected in a random sequence, but the pattern is more consistent with nonrandomness generated by DNA turnover mechanisms than with strand asymmetry due to a higher error rate on the lagging strand. 相似文献
69.
70.