首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   604篇
  免费   53篇
  2023年   5篇
  2022年   14篇
  2021年   20篇
  2020年   7篇
  2019年   9篇
  2018年   13篇
  2017年   15篇
  2016年   25篇
  2015年   30篇
  2014年   25篇
  2013年   37篇
  2012年   42篇
  2011年   33篇
  2010年   34篇
  2009年   27篇
  2008年   33篇
  2007年   40篇
  2006年   27篇
  2005年   18篇
  2004年   25篇
  2003年   28篇
  2002年   13篇
  2001年   12篇
  2000年   10篇
  1999年   10篇
  1998年   4篇
  1997年   5篇
  1996年   4篇
  1995年   3篇
  1994年   3篇
  1992年   3篇
  1991年   4篇
  1989年   5篇
  1988年   3篇
  1986年   3篇
  1985年   5篇
  1982年   2篇
  1980年   3篇
  1979年   5篇
  1978年   2篇
  1976年   4篇
  1975年   15篇
  1974年   8篇
  1973年   4篇
  1971年   2篇
  1967年   4篇
  1966年   3篇
  1964年   1篇
  1962年   1篇
  1944年   1篇
排序方式: 共有657条查询结果,搜索用时 140 毫秒
651.
The effects of olive leaf extract (OLE) are studied on several reproductive variables and the ovarian biochemical composition of Locusta migratoria (Orthoptera: Acrididae) adult females. The methanolic extracts are prepared from the leaves sampled during four phenological growth stages of olive tree: cluster formation (Cf), swelling inflorescence buds (Sib), full flowering (Ff) and endocarp hardening (Eh). When applied to adult females during the pre‐ovipositional phase, the treatment elicites a significant adverse effect on their reproductive potential. Indeed, OLE significantly reduces both fecundity and fertility and affects oocyte growth during the first gonadotrophic cycle, as indicated by measurements of ovarian weight, length of terminal oocytes and ovarian index. Furthermore, OLE is examined with respect to ovarian biochemical components. Biochemical analyses reveal a significant reduction of ovarian contents of proteins, lipids and carbohydrates, suggesting a disruption in the incorporation of the haemolymph metabolites in the oocytes and an interference of OLE with the vitellogenesis process. The antigonadotrophic effect is confirmed by a histological study of the ovaries, which clearly shows a delay in ovarian development and in yolk accumulation in the basal oocytes of treated females. The most effect is noted with the extract prepared from the leaves collected at the swelling inflorescence buds for all measured parameters, which appears to be related to its high content of polyphenols.  相似文献   
652.
We present in this paper the first report about identification of several fractions of phosphoglycerate mutase (PGlyM) activity using starch gel electrophoresis and two different buffer systems. A typical muscle form of PGlyM was detected. It is also shown that isozymes of phosphoglycerate kinase (PGK) can be separated through the buffer system used by Spencer et al; (1964) for the phosphogluco mutase.  相似文献   
653.
Kamel, M. Y. (Michigan State University, East Lansing), and R. L. Anderson. Metabolism of d-mannose in Aerobacter aerogenes: evidence for a cyclic pathway. J. Bacteriol. 92:1689-1697. 1966.-Evidence is presented which suggests a cyclic pathway for the constitutive utilization of d-mannose in extracts of Aerobacter aerogenes PRL-R3. d-Mannose is phosphorylated with d-glucose-6-phosphate to yield d-mannose-6-phosphate and d-glucose. d-Glucose-6-phosphate may be regenerated by isomerization of d-mannose-6-phosphate through d-fructose-6-phosphate, or by phosphorylation of d-glucose with adenosine-5'-triphosphate. The pathway involves the participation of four constitutive enzymes: d-glucose-6-phosphate isomerase, d-mannose-6-phosphate isomerase, a stereospecific d-glucokinase, and a phosphotransferase which phosphorylates d-mannose with d-glucose-6-phosphate, acetyl phosphate, or carbamyl phosphate. The absence of d-mannokinase (adenosine-5'-triphosphate:d-mannose phosphotransferase) activity in extracts of this organism suggests that the pathway may be of functional significance. Also, the pathway accounts for an apparent 2-epimerization of d-mannose to d-glucose that was observed in extracts.  相似文献   
654.
Purpose: To compare the T staging of potentially resectable esophageal cancer using free-breathing radial VIBE (r-VIBE) and breath-hold Cartesian VIBE (C-VIBE), with pathologic confirmation of the T stage. Materials and Methods: Fifty patients with endoscopically proven esophageal cancer and indeterminate T1/T2/T3 stage by CT scan were examined on a 3-T scanner. The MRI protocol included C-VIBE at 150 seconds post–IV contrast, immediately followed by a work-in-progress r-VIBE with identical spatial resolution (1.1 mm × 1.1 mm × 3.0 mm). Two independent readers assigned a T stage on MRI according to the 7th edition of UICC-AJCC TNM Classification, and postoperative pathologic confirmation was considered the gold standard. Interreader agreement was also calculated. Results: The T staging agreement between both VIBE techniques and postoperative pathologic T staging was 52% (26/50) for C-VIBE, 80% (40/50) for r-VIBE for reader 1, and 50% (25/50), 82% (41/50) for reader 2, respectively. For the esophageal cancer with invading lamina propria, muscularis mucosae, or submucosa (T1 stage), r-VIBE achieved 86% (12/14) agreement for both readers 1 and 2. For invasion of muscularis propria (T2 stage), r-VIBE achieved 83% (25/30) for both readers 1 and 2, whereas for the invasion of adventitia (T3 stage), r-VIBE could only achieve agreement in 50% (3/6) and 67% (4/6) for readers 1 and 2, respectively. Conclusion: Contrast-enhanced free-breathing r-VIBE is superior to breath-hold CVIBE in T staging of potentially resectable esophageal cancer, especially for T1 and T2.  相似文献   
655.
Three species, Zygophyllum album L., Z. coccineum L. and Z. simplex L., from family Zygophyllaceae were collected from two locations in Egypt to study their response to environmental conditions. Organic solutes (amino acids, soluble proteins and soluble sugars) and inorganic solutes (Na+, K+, Ca2+, Mg2+, Cl?, PO43? and SO42?) were estimated to study their role in osmotic adjustment under the effect of drought and salinity. The study showed that Z. coccineum is most tolerant for drought and salinity than Z. simplex. Z. coccineum was dependent on soluble proteins and soluble sugars, to increase its content of bound water, to undergo water deficit in desert. Z. simplex accumulated inorganic solutes more than Z. coccineum and less organic solutes. Amino acids content increased in Z. coccineum and Z. simplex survived in saline conditions to play a role in osmotic adjustment. Under the effect of salinity, all the studied species showed a tendency and high capacity to accumulate inorganic solutes. The main inorganic salutes were Ca2+, Mg2+ and Cl?. The role of Na+ was less than Ca2+ and Mg2+. Z. album and Z. simplex preferred Mg2+ more than Z. coccineum which preferred Ca2+.  相似文献   
656.
epi-Androsterone 1 was converted into its hydrazone derivative through the reaction with hydrazine hydrate 80%. Hydrazonoandrostane derivative 2b reacted with hydrazonoyl halides in the presence of K2CO3 forming the corresponding hydrazopyridazinoandrostane derivatives 6ad. The 3β-acetyl-17-hydrazonoandrostane derivative 2b reacted with a halogen reagent, benzoyl chloride, to form the non-cyclic 16-benzoylated hydrazone 9.On the other hand, compound 2b produced the corresponding pyridazinoandrostane derivatives 11 and 12 via its reaction with phenacyl bromide and chloroacetone respectively. Reaction of the hydrazono derivative 2b with benzaldehyde in the presence of acetic acid drops led to the formation of the benzylidenehydrazonoandrostane derivative 13. The product 14, phosphinom-ethylenehydrazonoandrostane was obtained by the reaction of the derivative 13 with trisdimethylaminophosphine in the presence of dry benzene. The reaction of compound 2b with phenyl isothiocyanate followed by boiling in chloroacetic acid or thioglycolic acid produced the pyrazoloandrostane derivatives 17 and 18 respectively. The biological activity of compounds 6a, 6d, 11, 12, and 15 was evaluated as inhibitor of growth in a human liver carcinoma cell line and doxorubicine was used for comparison. Compounds 15 and 12 showed a higher potency than the other tested compounds.  相似文献   
657.
A profile for molecular biology databases and information resources   总被引:1,自引:0,他引:1  
This paper examines the requirements for building database managementsystems and multi-database information resources to supportmolecular biology research. The paper profiles the most importantfeatures of 16 integrated resources and 102 databases relatedto molecular biology research. The aspects surveyed in thispaper include the nature of information in these databases,their sizes, update properties, cross-references, database managementsystem heterogeneity, geographical distribution, data quality,use of temporal information and level of interpretation. Thepaper also comments on the access patterns to these databases.Since not all these aspects were available for all databases,specific comparisons sometimes compare fewer than the full 102databases. Consequently, the same set of databases is not necessarilyalways being compared with respect to every aspect. The paperis organized primarily according to these comparison aspectsand ends with some concluding remarks.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号