全文获取类型
收费全文 | 11861篇 |
免费 | 1033篇 |
国内免费 | 18篇 |
专业分类
12912篇 |
出版年
2023年 | 51篇 |
2022年 | 130篇 |
2021年 | 199篇 |
2020年 | 131篇 |
2019年 | 168篇 |
2018年 | 223篇 |
2017年 | 219篇 |
2016年 | 325篇 |
2015年 | 585篇 |
2014年 | 595篇 |
2013年 | 742篇 |
2012年 | 955篇 |
2011年 | 834篇 |
2010年 | 546篇 |
2009年 | 531篇 |
2008年 | 794篇 |
2007年 | 670篇 |
2006年 | 619篇 |
2005年 | 565篇 |
2004年 | 539篇 |
2003年 | 485篇 |
2002年 | 461篇 |
2001年 | 207篇 |
2000年 | 184篇 |
1999年 | 166篇 |
1998年 | 126篇 |
1997年 | 92篇 |
1996年 | 71篇 |
1995年 | 106篇 |
1994年 | 67篇 |
1993年 | 69篇 |
1992年 | 106篇 |
1991年 | 90篇 |
1990年 | 91篇 |
1989年 | 95篇 |
1988年 | 96篇 |
1987年 | 89篇 |
1986年 | 77篇 |
1985年 | 91篇 |
1984年 | 64篇 |
1983年 | 57篇 |
1982年 | 49篇 |
1981年 | 41篇 |
1980年 | 46篇 |
1979年 | 49篇 |
1978年 | 58篇 |
1977年 | 41篇 |
1976年 | 48篇 |
1974年 | 42篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The inhibitory effect of trifluoroperazine (25-200 microM) on the sarcoplasmic reticulum calcium pump was studied in sarcoplasmic reticulum vesicles isolated from skeletal muscle. It was found that the lowest effective concentrations of trifluoroperazine (10 microM) displaces the Ca2+ dependence of sarcoplasmic reticulum ATPase to higher Ca2+ concentrations. Higher trifluoroperazine concentrations (100 microM) inhibit the enzyme even at saturating Ca2+. If trifluoroperazine is added to vesicles filled with calcium in the presence of ATP, inhibition of the catalytic cycle is accompanied by rapid release of accumulated calcium. ATPase inhibition and calcium release are produced by identical concentrations of trifluoroperazine and, most likely, by the same enzyme perturbation. These effects are related to partition of trifluoroperazine ino the sarcoplasmic reticulum membrane, and consequent alteration of the enzyme assembly within the membrane structure, and of the bilayer surface properties. The effect of trifluoroperazine was also studied on dissociated ('chemically skinned') cardiac cells undergoing phasic contractile activity which is totally dependent on calcium uptake and release by sarcoplasmic reticulum, and is not influenced by inhibitors of slow calcium channels. It was found that trifluoroperazine interferes with calcium transport by sarcoplasmic reticulum in situ, as well as with the role of sarcoplasmic reticulum in contractile activation. 相似文献
43.
Metabolic acidosis produces a phosphaturia which is independent of parathyroid hormone or dietary phosphorus intake. To study the underlying mechanism, inorganic phosphate (Pi) and glucose transport were studied in brush-border membrane vesicles prepared from the renal cortex of parathyroidectomized rats gavaged for three days with either 7.5 ml of 1.6% NaCl (control) or 1.5% NH4Cl (acidosis). At killing, blood pH and plasma bicarbonate were and , respectively, in control and () and () in acidotic rats. Serum Pi was similar in both groups, while 24 h urine Pi excretion was higher in the acidotic group (). Peak sodium-dependent uptake of Pi, measured after 1.5 min of incubation, was higher in controls than acidotic rats ( vs. protein, ), whereas peak glucose uptake at 1.5 min was not significantly different between the groups. Equilibrium values for Pi and glucose uptake were similar in the two groups. for Pi uptake in the control and acidotic animals were not different, 0.036 and 0.040 mM, respectively. By contrast, was higher in controls than in the acidotic group, 3.13 vs. 1.15 nmol/mg protein per 15 s. These results suggest that metabolic acidosis directly inhibits Pi uptake by the brush border of the proximal tubule by decreasing the availability of Pi carriers of the renal brush-border membrane. 相似文献
44.
Three photosynthetic enzymes were characterised in extractsfrom leaves and aerial roots of Aranda Christine 130.The enzymes from both tissues were similar in activity and kineticproperties. Grana-containing chloroplasts were found in rootcells of Vanda suauis. Thus components crucial to photosynthesisare present in aerial roots of these leafy orchids. (Received March 22, 1983; Accepted July 7, 1983) 相似文献
45.
Population dynamics of microfilarial production and eosinophilic levels in slow lorises infected with Breinlia sergenti, Petter (Filarioidea: Dipetalonematidae). International Journal for Parsitology 4: 383388. Observations have been made on microfilarial and eosinophilic levels in slow lorises infected with Breinlia sergenti. Animals given a single inoculation of 100-150 infective larvae exhibited three different patterns of microfilaraemia while superinfected animals showed enhanced microfilarial levels. It appeared that the number of inoculations as well as the interval between inocula are important factors in enhancing microfilarial levels. Two different types of incubation periods were seen, one at 100-120 days and the other at 200 days. The eosinophilic levels were investigated in some of the animals and an attempt was made to correlate these levels with the microfilaraemia. Cortisone injection appeared to promote a vigorous eosinophilia in some of the infected animals tested. 相似文献
46.
Comparison of the requirements for ribonucleic acid synthesis with the requirements for deoxyribonucleic acid synthesis in animal tissues 总被引:2,自引:0,他引:2
Ribonucleic acid polymerase and deoxyribonucleic acid polymerase have been partially purified from bovine lymphosarcoma, lymph node, and thymus. An examination of the deoxyribonucleic acid requirements of the two enzymes indicates that “native” deoxyribonucleic acid is the preferred template for ribonucleic acid synthesis; heat-denatured deoxyribonucleic acid is considerably less active. The primer requirements for deoxyribonucleic acid synthesis differ: “native” deoxyribonucleic acid is usually inactive, while denatured deoxyribonucleic acid is active. The two enzymes also differ in pH optima and in their requirements for metal cofactors. 相似文献
47.
48.
49.
Previously existing methods for determining the pH limits for the growth of microorganisms have involved (1), the setting up of individual cultures, each having a specific pH; (2), the pH gradient plate technique devised by Sacks (1956) in which a continuous pH gradient is established in a Petri dish by means of a buffer system; and (3), the pH gradient plate technique of Zak (unpublished), in which a continuous pH gradient is established by means of an electric current. The discontinuous pH gradient technique described here provides a convenient method of determining the maximum and minimum pH at which a microorganism can grow. The technique can be used aerobically or anaerobically, and has a precision of about ± 0.1 pH unit. Data are given for several yeasts and forSerratia marcescens. In all cases, the organisms tested continued to metabolize at pH values beyond those representing the limits for growth, sometimes by as much as 0.5 pH unit. The results suggest that pH limits are unsuitable criteria in microbial classification. 相似文献
50.
R W Butcher R J Ho H C Meng E W Sutherland 《The Journal of biological chemistry》1965,240(11):4515-4523