全文获取类型
收费全文 | 2317篇 |
免费 | 225篇 |
国内免费 | 1篇 |
专业分类
2543篇 |
出版年
2021年 | 31篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 32篇 |
2017年 | 16篇 |
2016年 | 43篇 |
2015年 | 87篇 |
2014年 | 106篇 |
2013年 | 134篇 |
2012年 | 115篇 |
2011年 | 128篇 |
2010年 | 86篇 |
2009年 | 65篇 |
2008年 | 108篇 |
2007年 | 115篇 |
2006年 | 100篇 |
2005年 | 116篇 |
2004年 | 102篇 |
2003年 | 85篇 |
2002年 | 83篇 |
2001年 | 42篇 |
2000年 | 36篇 |
1999年 | 42篇 |
1998年 | 32篇 |
1997年 | 18篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 27篇 |
1992年 | 37篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 15篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 15篇 |
1974年 | 18篇 |
1973年 | 18篇 |
1971年 | 25篇 |
1970年 | 14篇 |
排序方式: 共有2543条查询结果,搜索用时 0 毫秒
71.
Summary A mathematical model is presented for phase locking of a biological oscillator to a sinusoidal stimulus. Analytical, numerical and topological considerations are used to discuss the patterns of phase locking as a function of the amplitude of the sinusoidal stimulus and the relative frequencies of the oscillator and the sinusoidal stimulus. The sorts of experimental data which are needed to make comparisons between theory and experiment are discussed. 相似文献
72.
The cytochrome reductase system solubilized from microsomes exhibits monophasic reduction kinetics over the temperature range 15 ° to ?25 °C in aqueous/ethylene glycol co-solvent, whereas in intact microsomes, the process becomes increasingly heterogeneous below 0 °C, reflecting heterogeneities in membrane structure observable as distributions in reaction rates and activation energies. 相似文献
73.
The synergistic effect of exogenous cobra phospholipase A2 on the hemolysis rate of guinea pig erythrocytes by highly purified snake venom cardiotoxins was investigated. In the presence of phospholipase A2 the reaction was not only faster and had a lower activation energy but followed a sigmoidal instead of a linear time course. Similar results were obtained using porcine pancreatic phospholipase A2. Significantly, addition of even a trace of cobra phospholipase A2 (approx. 0.1%, w/w) was sufficient to bring about the full synergistic effect, emphasizing the stringent purity requirements for any meaningful investigation of cardiotoxin's own action. The possibility that the action of cardiotoxin on its own may involve the stimulation of an endogenous phospholipase is discussed in the light of the results obtained with exogenous cobra enzyme. 相似文献
74.
The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCL content of the sulfanilamide reagent. 相似文献
75.
The permeability of the blood-brain barrier to several classes of compounds was studied in rats between the ages of 15 days and 9 weeks. 14C-labelled test substances were injected simultaneously with two reference isotopes, 3H2O and 113mIn-labelled EDTA, into the common carotid artery followed by decapitation 10 s later.There was evidence that a monocarboxylic acid transport system in 15 to 23 day-old rats had a capacity at least six times greater than that present in adult animals. l-Lactate and acetate showed the highest permeability. At all ages there was a constant ratio between l-lactate and (−)d-3-hydroxybutyrate values. d-Glucose permeability increased with age, while that of several amino acids tested was the same in young and adults rats. 相似文献
76.
Harvey J. Berger Leon Speroff Steven Wolfson 《Prostaglandins & other lipid mediators》1976,11(3):499-502
Venous prostaglandins A, E, and F were determined by radioimmunoassay in 10 dogs before and one hour after administration of sodium pentobarbital (35 mg/Kg, iv). In the conscious state, PGA was 0.34 ± 0.04 ng/ml (mean ± SE), PGE 0.20 ± 0.01 ng/ml, and PGF 0.25 ± 0.03 ng/ml. During pentobarbital anesthesia, these levels were unchanged (p >0.05). Thus, pentobarbital anesthesia had no effect on peripheral venous prostaglandin levels. 相似文献
77.
The role of the adrenal gland in suppressing the onset of maternal behavior in virgin female rats was investigated. Virgin female rats were either ovariectomized, adrenalectomized, or subjected to the combined operation and tested for the induction of maternal behavior by being exposed to young pups. Females that were both ovariectomized and adrenalectomized 4 weeks prior to testing exhibited significantly shorter latencies to the onset of maternal behavior than that of females subjected to either ovariectomy or adrenalectomy alone. Replacement of either estrogen or progesterone in the group that was both adrenalectomized and ovariectomized resulted in a prolongation of the average latency to become maternal. The results indicated that both estrogen and progesterone can act to inhibit the onset of maternal behavior and that the adrenal gland may act to suppress the onset of such behavior by supplying an extra-ovarian source of endogenous progesterone and estrogen. 相似文献
78.
79.
Leon Salganicoff Patricia A. Hebda John Yandrasitz Miriam H. Fukami 《Biochimica et Biophysica Acta (BBA)/General Subjects》1975,385(2):394-411
Subcellular components were obtained from pig platelets, disrupted by means of a French press and separated into 4 primary fractions. The granule fraction (10 000 g) was subjected to a sucrose gradient fractionation. Primary fractions and the granule subfractions were studied electron microscopically and biochemically by following the distribution of markers of membranes, lysosomes of α-granules, mitochondria and dense granules. With this technique of platelet homogenization, 80% of the serotonin and 93% of the β-N-acetylglucosaminidase were found to be particulate. In the gradient, mitochondria were sharply banded in a fraction (density 1.16–1.17) having a specific activity 10–100 times higher than the other fractions of the gradient. Serotonin-containing granules were found in a pellet of density greater than 1.27 and contained 60% of the serotonin and adenine nucleotides of the granule fraction. The lysosome markers that were monitored, acid phosphatase and β-N-acetylglucosaminidase, exhibited different distribution patterns. Acid phosphatase showed the highest specific activity in the microsomal fraction with only 2.8% in the granule fraction, and this latter amount also appeared to be associated with membranes upon further fractionation. β-N-Acetylglucosaminidase was present in both the granule fraction and in the microsomal fraction with nearly the same specific activity. However, that present in the granule fraction was clearly associated with granules that distributed over a wide range of densities on a sucrose gradient. The calcium distribution was followed to attempt to determine its subcellular location; 19% was found in the same subfraction as the serotonin-containing granules, but at least 50% of the particulate calcium was associated with granules distinctly separate from the storage granules. 相似文献
80.
Jeffrey B. Smith Paul C. Sternweis Leon A. Heppel 《Journal of cellular biochemistry》1975,3(3):248-255
We have partially purified active delta and epsilon subunits of the E. coli membranebound Mg2+ -ATPase (ECF1). Treating purified ECF1 with 50% pyridine precipitates the major subunits (α, β, and γ) of the enzyme, but the two minor subunits (δ and ϵ), which are present in relatively small amounts, remain in solution. The delta and epsilon subunits were then resolved from one another by anion exchange chromatography. The partially purified epsilon strongly inhibits the hydrolytic activity of ECF1. The epsilon fraction inhibits both the highly purified five-subunit ATPase and the enzyme deficient in the δ subunit. The latter result indicates that the delta subunit is not required for inhibition by epsilon. By contrast, two-subunit enzyme, consisting chiefly of the α and β subunits, was insensitive to the ATPase inhibitor, suggesting that the γ subunit may be required for inhibition by epsilon. The partially purified delta subunit restored the capacity of ATPase deficient in delta to recombine with ATPase-depleted membranes and to reconstitute ATP-dependent transhydrogenase. Previously we reported (Biochem. Biophys. Res. Commun. 62:764 [1975]) that a fraction containing both the delta and epsilon subunits of ECF1 restored the capacity of ATPase missing delta to recombine with depleted membranes and to function as a coupling factor in oxidative phosphorylation and for the energized transhydrogenase. These reconstitution experiments using isolated subunits provide rather substantial evidence that the delta subunit is essential for attaching the ATPase to the membrane and that the epsilon subunit has a regulatory function as an inhibitor of the ATPase activity of ECF1. 相似文献