全文获取类型
收费全文 | 9544篇 |
免费 | 508篇 |
国内免费 | 8篇 |
出版年
2022年 | 28篇 |
2021年 | 86篇 |
2020年 | 56篇 |
2019年 | 82篇 |
2018年 | 118篇 |
2017年 | 102篇 |
2016年 | 150篇 |
2015年 | 259篇 |
2014年 | 315篇 |
2013年 | 632篇 |
2012年 | 547篇 |
2011年 | 538篇 |
2010年 | 351篇 |
2009年 | 357篇 |
2008年 | 569篇 |
2007年 | 552篇 |
2006年 | 531篇 |
2005年 | 606篇 |
2004年 | 591篇 |
2003年 | 558篇 |
2002年 | 519篇 |
2001年 | 169篇 |
2000年 | 163篇 |
1999年 | 167篇 |
1998年 | 150篇 |
1997年 | 118篇 |
1996年 | 106篇 |
1995年 | 106篇 |
1994年 | 73篇 |
1993年 | 88篇 |
1992年 | 142篇 |
1991年 | 111篇 |
1990年 | 85篇 |
1989年 | 107篇 |
1988年 | 81篇 |
1987年 | 82篇 |
1986年 | 69篇 |
1985年 | 66篇 |
1984年 | 70篇 |
1983年 | 59篇 |
1982年 | 55篇 |
1981年 | 45篇 |
1980年 | 29篇 |
1979年 | 51篇 |
1978年 | 46篇 |
1977年 | 41篇 |
1976年 | 34篇 |
1975年 | 31篇 |
1974年 | 25篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
A major isozyme of rat heart glutathione transferase was purified to homogeneity by Sephadex G-200 gel filtration, ammonium sulfate precipitation, CM-cellulose chromatography and affinity chromatography on S-hexylglutathione-linked Sepharose 6B. The purified isozyme was a dimer with an apparent relative molecular mass of 50 000 composed of two Yb-size subunits (Mr = 26 500). The isozyme is immunologically related to rat liver glutathione transferase X and 3-3, especially closely to transferase X, and no immunological cross-reactivity with subunits 1 and 2 of hepatic glutathione transferases was observed. The isoelectric point (pI = 6.9) of the isozyme was identical with and the substrate specificity was very similar to transferase X. Thus, the cardiac near-neutral isozyme is considered to be identical to glutathione transferase X recognized in rat liver. The amount of this near-neutral isozyme estimated to be present in heart tissue is 70 micrograms/g. The isozyme has relatively high activities towards alpha, beta-unsaturated carbonyl compounds such as trans-4-phenyl-3-buten-2-one and trans-4-hydroxynon-2-enal. The latter is a cytotoxic product resulting from lipid peroxidation of polyunsaturated fatty acids, and the cardiac isozyme may play a physiologically significant role with glutathione conjugation of this compound. In addition to the near-neutral isozyme, acidic forms with isoelectric points of 4.9, 5.2 and 5.5 were partially purified; some of them are considered to consist of subunits immunologically related to transferase X. 相似文献
73.
Structure of the trypsin-binding domain of Bowman-Birk type protease inhibitor and its interaction with trypsin 总被引:7,自引:0,他引:7
Y Tsunogae I Tanaka T Yamane J Kikkawa T Ashida C Ishikawa K Watanabe S Nakamura K Takahashi 《Journal of biochemistry》1986,100(6):1637-1646
The crystal structure of the complex formed by bovine trypsin and Bowman-Birk type protease inhibitor AB-I extracted from azuki beans (Vigna angularis) 'Takara' has been analyzed. The structure was solved by the application of the phase combination of single isomorphous phases and trypsin model phases, followed by phase improvement using the iterative Fourier technique. From the resulting electron density map, a three-dimensional atomic model of the trypsin binding domain of AB-I has been built. The peptide chain at the trypsin reactive site turns back sharply at Pro29 and forms a 9-residue ring (Cys24-Cys32). The 'front side' of this ring, consisting of the reactive site (Cys24-Met28), interacts with trypsin in a similar manner to other families of inhibitors and forms a stable complex, which seems to be maintained by the interactions with the 'back side' of this ring (Pro29-Cys34). The similar spatial arrangements of the 'back side' of this inhibitor and the 'secondary contact region' of the other inhibitors with respect to the reactive site suggest an important common role of these regions in exhibiting inhibitory activity. 相似文献
74.
Tatsuhide Kunishita Takeshi Tabira Hidehiko Umezawa Makoto Mizutani Yasutomi Katsuie 《Journal of neurochemistry》1986,46(1):105-111
Biochemical and morphological studies were done on a new trembling mutant hamster CBB. The yield of myelin from the mutant was 30 and 40% of the control at 46 and 140 days of age, respectively, but myelin composition and 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNPase) activity were normal. Morphologically, about 18% of the axons were myelinated in the mutant optic nerve at 46 days of age, in which the myelinated fibers were those with larger diameters (more than 0.6 micron), while the control had a peak at 0.4 micron in diameter. The ultrastructure and thickness of compact myelin lamellae in the mutant were normal. Myelination and the structure of peripheral nerve myelin appeared normal. The results indicate that the essential defect is the delay and arrest of myelination in the CNS, which is probably caused by either a decreased rate of synthesis of myelin components in oligodendrocytes or a defect in the oligodendrocyte-axon recognition in smaller axons. 相似文献
75.
(6R)-Tetrahydrobiopterin Increases the Activity of Tryptophan Hydroxylase in Rat Raphe Slices 总被引:2,自引:2,他引:0
Makoto Sawada Takashi Sugimoto Sadao Matsuura Toshiharu Nagatsu† 《Journal of neurochemistry》1986,47(5):1544-1547
The effects of (6R)- and (6S)-tetrahydrobiopterin (BPH4), tetrahydroneopterin, and 6-methyltetrahydropterin on the activity of tryptophan hydroxylase were investigated in rat raphe slices. The activity of tryptophan hydroxylase was estimated by measurement of 5-hydroxytryptophan (5-HTP) formation under inhibition of aromatic L-amino acid decarboxylase with use of HPLC-fluorometric detection. (6R)-BPH4 (the naturally occurring form) at 42 microM, tetrahydroneopterin at 50 microM, and 6-methyltetrahydropterin at 100 microM increased tryptophan hydroxylase activity to 350, 145, and 146% of control values, respectively. (6S)-BPH4, however, had no significant effects on tryptophan hydroxylase activity. These results suggest that tryptophan hydroxylase is subsaturating in vivo for the naturally occurring cofactor, (6R)-BPH4, and that the concentration of (6R)-BPH4 may play an important role for the regulation of tryptophan hydroxylase activity in vivo. 相似文献
76.
Yutaka Suzuki Yoshiteru Harada Akinori Ueno Makoto Katori Haruya Okabe 《Prostaglandins & other lipid mediators》1986,32(3)
Filling of the gastric lumen of rats with 1.0 M NaCl solution (5 ml) for 10 min under urethane anesthesia caused an increase in the gastric fluid concentrations of prostaglandin (PG) E2, 13, 14-dihydro-15-keto-PGE2 and 6-keto-PGF1α as determined by radioimmunoassay. PGE2 was the major PG generated. The levels of PGE2 in the gastric fluid were increased dose-dependently after filling the lumen with 0.3, 0.5, 0.7 or 1.0 M NaCl solutions. The pH of the gastric fluid increased similarly after 0.5 to 1.0 M NaCl solutions. Indomethacin (10 mg/kg, i.p.) suppressed the PGE2 increase caused by 1.0 M NaCl solution, but did not prevent the increase of the pH of the gastric fluid induced by intragastric 1.0 M NaCl. Infusion of tetragastrin (62.5 μg/kg/hr, i.v., for 10 min) caused a marked increase of acid secretion without modifying intragastic concentration of PGE2. The acid secretion due to tetragastrin was completely inhibited after intragastric administration of 1.0 M NaCl solution, while indomethacin restored the tetragastrin-induced acid secretion, with prevention of a rise of intragastric PGE2 levels. These observations suggest that 1.0 M NaCl solutions suppress basal intragastric acid through a mechanism which is independent of prostaglandins. In contrast, the suppression of tetragastrin-induced acid secretion by intragastric 1.0 M NaCl solution appears to be mediated through a release of prostaglandins 相似文献
77.
Atrial natriuretic factor increases cyclic GMP and inhibits cyclic AMP in rat renal papillary collecting tubule cells in culture 总被引:3,自引:0,他引:3
S Ishikawa T Saito K Okada T Kuzuya K Kangawa H Matsuo 《Biochemical and biophysical research communications》1985,130(3):1147-1153
The present study was undertaken to determine whether human atrial natriuretic factor (hANF) produces guanosine-3', 5'-monophosphate (cGMP) and alters arginine vasopressin (AVP)- and forskolin (F)- induced adenosine-3', 5'-monophosphate (cAMP) production in the cultured rat renal papillary collecting tubule cells. hANF increased cellular cGMP levels in a dose dependent manner. AVP and F, however, did not affect cGMP production. hANF significantly inhibited AVP- and F-stimulated cAMP levels, but hANF by itself did not affect cellular cAMP production. Since F activates adenylate cyclase at a step of catalytic unit and the cellular action of AVP to activate adenylate cyclase is mediated through receptor-catalytic units, the present results indicate that hANF may directly inhibit the AVP- and F-stimulated adenylate cyclase in renal papillary collecting tubules. 相似文献
78.
A simple and sensitive procedure was developed for the simultaneous determination of substances metabolically related to monoamine transmitters including 3-methoxy-4-hydroxy-phenylethylene glycol (MOPEG) in dissected brain regions of rats using high-performance liquid chromatography combined with electrochemical detection. The tissue sample was homogenized in HCl solution. The homogenate was divided into two portions, of which one was used for the assay of MOPEG after enzymatic hydrolysis with sulfatase. A butanol extraction process was performed on the remaining portion to obtain the sample of monoamine transmitters, precursor amino acids, and acidic metabolites. The monoamines and precursor amino acids were finally recovered in HCl solution, while the acidic metabolites shifted into the alkaline buffer from the organic layer. The basic and neutral substances were separated with a 0.1 M sodium citrate/citric acid buffer system (pH 4.0) containing 1% tetrahydrofuran, and the acidic ones with 0.075 M sodium citrate/citric acid buffer (pH 3.5) containing 1% tetrahydrofuran, 10% methanol, and 12% acetic acid. The steady-state concentrations of three monoamine transmitters (noradrenaline, dopamine, and 5-hydroxytryptamine) were determined together with their precursors and metabolites. Changes in the concentrations of these substances were examined for various drugs, of which the effects had been previously confirmed. The changes reflected putative drug effects and demonstrated that the procedure was applicable to the regional determination of monoamines and their metabolically related substances. 相似文献
79.
The binding of lipophilic ions to the membrane of envelope vesicles from Halobacterium halobium was examined in the absence and presence of membrane potential. The lipophilic ions used constitute a homologous series of (Phe)3-P+-(CH2)n-CH3 (n = 0–4) and tetraphenylphosphonium (TPP+). In the absence of membrane potential, the amounts of binding were proportional to the probe concentration in the medium when the concentration is dilute. Upon illumination, interior negative membrane potential is generated which induces the uptake of phosphonium cation probe. 2 μM were employed as the initial probe concentration. The real membrane potential was evaluated by means of extrapolation to the state of no binding: The values of
for various probes are plotted against the binding coefficient. Here, Ciapp is the apparent intra-vesicular concentration of the probes which is calculated without consideration of bound probes. The ordinate intercept of the plot gives the true concentration ratio, and from this the membrane potential is evaluated. The membrane potential-dependent binding was analysed with a model: the membrane is split into two halves, outer and inner half, and the amounts of bound probes in each region are governed by the concentration in the contiguous solution. We obtained a formula which describes amounts of binding as a function of the membrane potential. 相似文献
80.
Activated c-raf gene in a rat hepatocellular carcinoma induced by 2-amino-3-methylimidazo[4,5-f]quinoline 总被引:8,自引:0,他引:8
F Ishikawa F Takaku M Ochiai K Hayashi S Hirohashi M Terada S Takayama M Nagao T Sugimura 《Biochemical and biophysical research communications》1985,132(1):186-192
A rat hepatocellular carcinoma, IQ7, induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) gave two transformants of NIH 3T3 cells on DNA mediated gene transfer. One of these transformants was examined further and secondary and tertiary transformants were obtained. The secondary transformant was tumorigenic in nude mice. The activated oncogene in this primary transformant was identified as rat c-raf by Southern blot analysis. 相似文献