全文获取类型
收费全文 | 134685篇 |
免费 | 15310篇 |
国内免费 | 642篇 |
专业分类
150637篇 |
出版年
2021年 | 1295篇 |
2019年 | 1046篇 |
2018年 | 1506篇 |
2017年 | 1408篇 |
2016年 | 1913篇 |
2015年 | 2711篇 |
2014年 | 3111篇 |
2013年 | 3895篇 |
2012年 | 4695篇 |
2011年 | 4564篇 |
2010年 | 2985篇 |
2009年 | 2869篇 |
2008年 | 3782篇 |
2007年 | 3715篇 |
2006年 | 3515篇 |
2005年 | 3287篇 |
2004年 | 3220篇 |
2003年 | 3140篇 |
2002年 | 3082篇 |
2001年 | 10100篇 |
2000年 | 9873篇 |
1999年 | 7588篇 |
1998年 | 1899篇 |
1997年 | 2001篇 |
1996年 | 1789篇 |
1995年 | 1637篇 |
1994年 | 1492篇 |
1993年 | 1405篇 |
1992年 | 5026篇 |
1991年 | 4735篇 |
1990年 | 4173篇 |
1989年 | 4208篇 |
1988年 | 3765篇 |
1987年 | 3233篇 |
1986年 | 2910篇 |
1985年 | 2834篇 |
1984年 | 2120篇 |
1983年 | 1843篇 |
1982年 | 1344篇 |
1981年 | 1081篇 |
1980年 | 1012篇 |
1979年 | 1851篇 |
1978年 | 1458篇 |
1977年 | 1282篇 |
1976年 | 1079篇 |
1975年 | 1216篇 |
1974年 | 1222篇 |
1973年 | 1218篇 |
1972年 | 1070篇 |
1971年 | 994篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
S Kim S Morimoto E Koh Y Miyashita T Ogihara 《Biochemical and biophysical research communications》1989,164(3):1003-1008
The effects of a potassium (K+) channel opener BRL34915 and a specific K+ ionophore valinomycin on vasoconstriction induced by endothelin (ET) were compared with those of calcium (Ca2+) channel blockers, nicardipine and verapamil, using helical strips from rat thoracic aorta. ET induced potent and persistent contraction in control solution and similar but smaller contraction in Ca2+-free solution. BRL34915 and valinomycin inhibited the ET-induced contraction dose-dependently in control solution, but not in Ca2+-free solution. The ET-induced contraction was also inhibited by nicardipine and verapamil, though less strongly. On the other hand, high K+ (35 mM)-induced vasoconstriction was strongly inhibited by nicardipine and verapamil, but not by BRL34915 or valinomycin. These results support the idea that the extracellular Ca2+-dependent component of the ET-induced contraction may be mediated by Ca2+ influx by a route other than voltage-dependent Ca2+-channels. 相似文献
982.
Interleukin-1 inhibits the secretion of gastric acid in rats: possible involvement of prostaglandin 总被引:5,自引:0,他引:5
A Uehara T Okumura C Sekiya K Okamura Y Takasugi M Namiki 《Biochemical and biophysical research communications》1989,162(3):1578-1584
To examine the hypothesis that interleukin-1 may inhibit the secretion of gastric acid, the present study was carried out using pylorusligated rats. Based upon three lines of evidence, we report here that interleukin-1, both endogenously released and exogenously administered, suppresses gastric acid secretion and that the interleukin-1-induced inhibition of acid output is possibly mediated by prostaglandin. First, lipopolysaccharide, a potent stimulant of the release and production of endogenous interleukin-1, caused the suppression of gastric acid, and this response was dose-related. Second, the intraperitoneal injection of interleukin-1 resulted in a dose-related inhibition of gastric acid output. Third, the administration of indomethacin completely blocked the suppression of gastric acid secretion induced by interleukin-1. These results demonstrated for the first time that IL-1 might be involved in the regulation of gastric secretion. 相似文献
983.
Determination of immunoreactive endothelin in medium from cultured endothelial cells and human plasma 总被引:1,自引:0,他引:1
Y T Xuan A R Whorton E Shearer-Poor J Boyd W D Watkins 《Biochemical and biophysical research communications》1989,164(1):326-332
We have developed a sensitive and selective radioimmunoassay for porcine/human endothelin (ET1). The assay has a detection limit of 0.62 pg/tube and exhibits no cross-reactivity to atrial natriuretic peptide, arginine vasopressin, or angiotensin II. Procedures were developed for extraction of endothelin from human plasma samples and samples of buffer from endothelial cell incubations using C18 Sep-Pak extraction cartridges. The mean recovery following extraction was approximately 80%. Both bovine and porcine aortic endothelial cells were found to produce immunoreactive endothelin (IR-ET) with porcine cells producing 4.7 +/- 1.1 ng of IR-ET/mg cell protein after 6 hours. Human plasma samples were extracted, assayed and found to contain a mean concentration of 2.0 +/- 0.4 pg/ml of IR-ET. 相似文献
984.
Presence of endothelin-1 in porcine spinal cord: isolation and sequence determination 总被引:2,自引:0,他引:2
O Shinmi S Kimura T Yoshizawa T Sawamura Y Uchiyama Y Sugita I Kanazawa M Yanagisawa K Goto T Masaki 《Biochemical and biophysical research communications》1989,162(1):340-346
We investigated the molecular forms of endothelin (ET) related peptides in porcine spinal cord by high performance liquid chromatography coupled with radioimmunoassays using three antisera raised against ET-1 and C-terminal fragments of ET-1 and big ET-1. ET-1 and its oxidized form were isolated as major immunoreactive peptides and sequenced. Furthermore, immunoreactivities like ET-3 and big ET-1(22-39) (contents: less than 8% and less than 1% of ET-1, respectively) were detected based on their chromatographic retention times and characteristics of immunoreactivity to the antisera. Big ET-1 was only scarcely detected. Immunohistochemical study showed the presence of ET-1-like immunoreactivity in motoneurons, dorsal horn neurons and dot- and fiber-like structures in the dorsal horn of lumbar spinal cord. These results indicate that ET-1 is present not only in endothelial cells but also in spinal cord, and that big ET-1 is converted into ET-1 in spinal cord by specific processing between Trp21-Val22. The data also indicate that ET-1 may act as a neuropeptide in the central nervous system. 相似文献
985.
Functional endothelin/sarafotoxin receptors in the rat uterus 总被引:6,自引:0,他引:6
D Bousso-Mittler Y Kloog Z Wollberg A Bdolah E Kochva M Sokolovsky 《Biochemical and biophysical research communications》1989,162(3):952-957
Functional receptors for the peptides of the endothelin (ET) and sarafotoxin (SRTX) families were detected in the rat uterus. These receptors specifically bind 125I-SRTX-b (Bmax = 220 fmol/mg protein), as well as ET-1, ET-3 and SRTX-c (IC50's 10, 5, 300 and 780 nM, respectively). Activation of the uterine ET/SRTX receptors induced dose-dependent phosphoinositide (PI) hydrolysis and three typical contractile responses: 1) increase in the muscle tonic tension; 2) increase in frequency of the spontaneous rhythmic contractions; 3) decrease of relaxation in each spontaneous rhythmic cycle. All three effects appeared at doses as low as 0.5-1 nM. Dose responses yield ED50 values of 5.5, 30 and 680 nM for ET-1, SRTX-b and ET-3, respectively. SRTX-c was the least effective peptide in achieving decrease in relaxation. In view of these results, and since the uterine responses to the peptides were almost immediate and reversible, we suggest that the functional ET/SRTX receptor of the rat uterus that is coupled to PI hydrolysis may be of physiological significance. 相似文献
986.
The plasmid pSCR1 containing the gene for mandelate racemase (EC 5.1.2.2) from Pseudomonas putida (ATCC 12633) allows Pseudomonas aeruginosa (ATCC 15692) to grow on (R)-mandelate as its sole carbon source [Ransom, S. C., Gerlt, J. A., Powers, V. M., & Kenyon, G. L. (1988) Biochemistry 27, 540]; the chromosome of the P. aeruginosa host apparently does not contain the gene for mandelate racemase but does contain genes for the remaining enzymes in the mandelate pathway and enables growth on (S)-mandelate as carbon source. However, in the presence of alpha-phenylglycidate, an active-site-directed irreversible inhibitor (affinity label) of mandelate racemase, P. aeruginosa transformed with pSCR1 can utilize (S)-mandelate but not (R)-mandelate as carbon source. This inhibition of growth on (R)-mandelate provides a metabolic selection for mutants that are resistant to alpha-phenylglycidate. When (R)-mandelate is used as carbon source and alpha-phenylglycidate is present, a few colonies of P. aeruginosa transformed with pSCR1 grow slowly and appear on plates after several days. The plasmid isolated from these cells confers resistance to alpha-phenylglycidate on newly transformed cells of P. aeruginosa. This resistance to the affinity label is not due to a mutation within the primary structure of the enzyme. A single base change (C----A) located 87 bp upstream of the initiation codon for the gene for mandelate racemase was detected in three independent isolates of alpha-phenylglycidate-resistant colonies and appears responsible for a 30-fold increase in the amount of mandelate racemase encoded by the gene contained in the plasmid.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
987.
Effect of endothelin-1 on release of arginine-vasopressin from perifused rat hypothalamus 总被引:2,自引:0,他引:2
M Shichiri Y Hirata K Kanno K Ohta T Emori F Marumo 《Biochemical and biophysical research communications》1989,163(3):1332-1337
Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor peptide with potent pressor activity. We studied the effect of ET-1 on release of arginine-vasopressin (AVP) from perifused rat hypothalamus. ET-1 (10(-10) to 10(-8) M) significantly stimulated AVP release. The ET-1-induced AVP release was completely blocked in the presence of nicardipine. Our results suggest a possible involvement of ET in the regulation of AVP release. 相似文献
988.
New mutant alleles of theadenosine2 locus (ade2; 2–17.7) have been isolated using the eye-color phenotype exhibited by the prototype auxotrophic alleleade2
1 as the screening criterion. The new mutants form a single complementation group, suggesting that they all exhibit purine auxotrophy and defective formylglycineamide ribotide amidotransferase enzyme, likeade2
1. Tests carried out on particular new alleles confirm these suggestions. The new mutants all exhibit more extreme physical defects than the prototype. They have wing abnormalities like mutants defective in pyrimidine biosynthesis and reduced bristles like those defective in protein synthesis; thus they exhibit the combined visible phenotype ofrudimentary wings,rosy eyes, andbobbed bristles. Cytogenetic analysis places the locus in the interband proximal to26B1-2.This work was supported by NSERC Operating Grant A3269 to D.N., an Alberta Heritage Foundation for Medical Research Postdoctoral Fellowship to S.Y.K.T., and National Institute on Aging Grant AG00029 to D.P. 相似文献
989.
Y Saito K Nakao G Shirakami M Jougasaki T Yamada H Itoh M Mukoyama H Arai K Hosoda S Suga 《Biochemical and biophysical research communications》1989,163(3):1512-1516
Using two radioimmunoassays (RIAs) for endothelin-1 (ET-1) with and without a substantial cross-reactivity with ET-3, we have measured the plasma ET-1-like immunoreactivity (-LI) level in rat plasma. ET-1-LI was detected in plasma from male Wistar rats. ET-1-LI in rat plasma consisted of three components with molecular weights of 6K, 4K and 2.5K daltons by gel permeation chromatography. Two of the components were eluted at positions of big ET (4K) and synthetic ET-1 (2.5K). The remaining component was eluted at the preceding fraction (6K). No difference was observed in ET-1-LI of the small molecular form of ET (2.5K) between the two RIAs. Thus, there is little or no ET-3 in rat plasma, which has the sequence found originally in the rat genome. The concentration of the small molecular form of ET, presumably ET-1, in rat plasma was about 4 pg/ml. 相似文献
990.
Y Mouneimne P F Tosi Y Gazitt C Nicolau 《Biochemical and biophysical research communications》1989,159(1):34-40
The electroporation technique, with field strengths slightly below the critical value Ec for electroporation of red blood cells (RBC), enables the insertion of xeno-proteins into the RBC membrane without damaging the cells. The electro-insertion has been used to insert biotinylated human glycophorin into human RBC membrane and human glycophorin into murine RBC membrane. Binding anti-human glycophorin antibody (10F7) to the murine RBC bearing human glycophorin indicates extracellular orientation of inserted glycophorin. Insertion of about 10(5) glycophorin molecule per cell has been estimated by whole cell ELISA. 相似文献