全文获取类型
收费全文 | 131318篇 |
免费 | 2712篇 |
国内免费 | 862篇 |
专业分类
134892篇 |
出版年
2023年 | 244篇 |
2022年 | 224篇 |
2021年 | 510篇 |
2020年 | 463篇 |
2019年 | 455篇 |
2018年 | 12675篇 |
2017年 | 11353篇 |
2016年 | 8692篇 |
2015年 | 2501篇 |
2014年 | 2196篇 |
2013年 | 2866篇 |
2012年 | 7065篇 |
2011年 | 15200篇 |
2010年 | 13437篇 |
2009年 | 9336篇 |
2008年 | 11597篇 |
2007年 | 13137篇 |
2006年 | 2279篇 |
2005年 | 2164篇 |
2004年 | 2599篇 |
2003年 | 2492篇 |
2002年 | 2163篇 |
2001年 | 1272篇 |
2000年 | 1140篇 |
1999年 | 798篇 |
1998年 | 311篇 |
1997年 | 223篇 |
1996年 | 225篇 |
1995年 | 224篇 |
1994年 | 169篇 |
1993年 | 171篇 |
1992年 | 466篇 |
1991年 | 427篇 |
1990年 | 375篇 |
1989年 | 368篇 |
1988年 | 335篇 |
1987年 | 326篇 |
1986年 | 287篇 |
1985年 | 281篇 |
1984年 | 230篇 |
1983年 | 217篇 |
1982年 | 161篇 |
1979年 | 249篇 |
1974年 | 174篇 |
1973年 | 170篇 |
1972年 | 408篇 |
1971年 | 425篇 |
1970年 | 164篇 |
1969年 | 160篇 |
1968年 | 153篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
D M Rice M D Meadows A O Scheinman F M Go?i J C Gómez-Fernández M A Moscarello D Chapman E Oldfield 《Biochemistry》1979,18(26):5893-5903
Deuterium Fourier transform nuclear magnetic resonance (NMR) spectra at 34 MHz (corresponding to a magnetic field strength of 5.2 T) have been obtained of a variety of protein-lipid systems containing specifically deuterated phospholipids. The following systems were investigated as a function of temperature: sarcoplasmic reticulum ATPase (ATP phosphohydrolase, EC 3.6.1.3) complexed with 1-myristoyl-2-(14,14,14-trideuteriomyristoyl)-sn-glycero-3-phosphocholine (DMPC-d3) or 1,2-bis(16,16,16-trideuteriopalmitoyl)-sn-glycero-3-phosphocholine (DPPC-k6); human brain lipophilin complexed with DPPC-d6 or 1,2-bis(6,6-dideuteriopalmitoyl)-sn-glycero-3-phosphocholine (DPPC-6,6-d4); beef brain myelin proteolipid apoprotein (PLA) reconstituted with DMPC labeled as CD2 (or CD3) at one or more of positions 3, 4, 6, 8, 10, 12, or 14 of the sn-2 chain. For purposes of comparison, spectra were also obtained for bilayers containing cholesterol (CHOL). The results show that proteins either disorder or have little effect on hydrocarbon chain order in membranes above the gel to liquid-crystal phase transition temperature (Tc) of the pure lipids. Cholesterol, however, causes a very large ordering of the hydrocarbon chains above Tc, but both cholesterol and protein prevent chain crystallization (by effectively disordering chain packing) immediately below Tc. No evidence for any ordered "boundary lipid" in association with protein was found above Tc, perhaps due to the rough nature of protein surfaces. Above Tc, exchange between free bilayer and protein associated lipid is fast on the time scale of the deuterium NMR experiment (greater than or similar to 10(3) s-1). We have also obtained proton-decoupled phosphorus-31 nuclear magnetic resonance spectra at 60.7 MHz (corresponding to a magnetic field strength of 3.5 T) of DMPC, DMPC-AT-Pase, and DMPC-CHOL complexes. The results indicate that ATPase and CHOL CAUSE SMALL DECREASES IN 31P chemical shielding anisotropies but that in addition ATPase causes a four- to fivefold increase in 31P spin-lattice and Carr-Purcell spin-spin relaxation rates, suggesting the possibility of polar group protein-lipid interaction leading to increased correlation times in the region of the lipid phosphate head group. 相似文献
872.
873.
874.
875.
The configuration of brain mitochondria was compared in situ, after aldehyde perfusion and/or osmium immersion fixation and in isolated fractions of different functional performance. After combined aldehyde perfusion osmium immersion fixation in situ, mitochondria were condensed having a dark matrix. Fractions capable of controlled respiration also consisted of condensed mitochondria. On the contrary, expanded mitochondria with light matrix were brought about by immersion fixation. Fractions consisting predominantly of light mitochondria displayed no controlled respiration. Light matrix and expanded form are therefore regarded as a functionally impaired state of brain mitochondria. The condensed form is thought to be a landmark of good fixation. 相似文献
876.
877.
Summary The alary muscles of Locusta migratoria adults make up the major tissue of the dorsal diaphragm which separates pericardial and perivisceral sinuses in the abdomen. The alary muscles are striated with a sarcomere at rest measuring about 9 m. The Z-line has a staggered-beaded arrangement with A-bands and I-bands readily discernable. Thick myofilaments are surrounded by 10 or more thin filaments. The sarcoplasm has few mitochondria near the area of the Z-line, dyads are present and sarcoplasmic reticulum is poorly developed. Axons which innervate the alary muscle are either contained within invaginated folds of the sarcolemma of the muscle cells or the muscle cells send finger-like projections to envelop the axons. The synaptic terminals contain synaptic vesicles between 40 and 45 nm in diameter and a few electron-dense granules near or less than 170 nm in diameter. Away from synaptic terminals the axon profiles show few or no granules. The axons are accompanied everywhere by well-developed glial cells. This then is not typical neurosecretomotor innervation, however, the presence of electron-dense granules suggests the possibility of peptidergic neurotransmission. 相似文献
878.
An assay method for glyceraldehyde-3-phosphate dehydrogenase in which none of the primary products accumulate and which gives linear kinetics under physiological conditions has been developed. It is based on the use of the 1,3-diphosphoglycerate produced by the enzyme for the formation of NADPH, while the NADH produced is recycled with an auxiliary system. Revised Km values at pH 7.4 for the muscle (rabbit and rat) enzyme are: glyceraldehyde-3-P, 50 μM; NAD, 100 μM; Pi, 10 mM. The rat erythrocyte enzyme gave similar values except for glyceraldehyde-3-P which was 300 μM. Cooperativity for NAD+ tends to be positive but is a variable parameter. 相似文献
879.
The endotoxin of Bordetella pertussis was cleaved by mild acidic hydrolysis to yield a polysaccharide (polysaccharide I, 15%), a glycolipid (63%) and lipid X (2%). Further treatment of the glycolipid with stronger acid released a second polysaccharide (polysaccharide II, 9%) and material similar to lipid A present in enterobacterial endotoxins. Both polysaccharides possess a single molecule of 3-deoxy-2-octulosonic acid as the reducing, terminal sugar. In polysaccharide II the octulosonic acid is phosphorylated in position 5 and presumably substituted in position 4; in polysaccharide I the octulosonic acid is not phosphorylated, but is substituted in position 5. Following treatment of the endotoxin with strong base, a fragment was isolated that contained bound, non-phosphorylated 3-deoxy-2-octulosonic acid, glucosamine phosphate and fatty acids. This indicated that polysaccharide I, like polysaccharide II, was bound to the lipid region of the endotoxin. The endotoxin structure thus defined is different from that proposed for the lipopolysaccharides of enterobacteria. 相似文献
880.
Cercariae of Schistosoma mansoni were treated with undecenyl-pseudothiourea. After centrifugation, they agglutinated into a mass. Resuspended in water, they remained immobilized. When injected sub-cutaneously into mice, they produced bisexual infections. The immobilizing drug effect, together with a reduced worm recovery rate, are time and concentration dependent. The cercariae become avirulent (99.8%) only when the flame cell is affected. Immobilizing and “cercaricidal” effects are not necessarily related properties; the latter can be determined only by in vivo tests of infectivity. No protection against reinfection was noticed in mice injected with immobilized cercariae of reduced virulence. The immobilized cercariae produced infections with a 0.7% worm recovery rate by percutaneous exposure, compared to 2.2% by subcutaneous injection. Normal cercariae produced infections with average recovery rates of 11.1% subcutaneously and 45% percutaneously. 相似文献