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   1810篇
  免费   85篇
  2023年   20篇
  2022年   13篇
  2021年   64篇
  2020年   52篇
  2019年   54篇
  2018年   50篇
  2017年   61篇
  2016年   78篇
  2015年   82篇
  2014年   103篇
  2013年   129篇
  2012年   139篇
  2011年   150篇
  2010年   94篇
  2009年   72篇
  2008年   101篇
  2007年   106篇
  2006年   91篇
  2005年   79篇
  2004年   72篇
  2003年   55篇
  2002年   50篇
  2001年   18篇
  2000年   17篇
  1999年   18篇
  1998年   14篇
  1997年   5篇
  1996年   5篇
  1995年   3篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1991年   4篇
  1990年   7篇
  1989年   3篇
  1988年   6篇
  1987年   3篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1983年   3篇
  1982年   3篇
  1977年   3篇
  1975年   4篇
  1974年   5篇
  1973年   10篇
  1972年   3篇
  1971年   5篇
  1970年   5篇
  1967年   2篇
排序方式: 共有1895条查询结果,搜索用时 281 毫秒
991.
A series of novel indenopyrazole derivatives 2a‐j and 3a‐j were synthesized from the reaction of 1‐(4‐(hydroxy(1‐oxo‐1,3‐dihydro‐2 H‐inden‐2‐ylidene)methyl)phenyl)‐3‐phenylurea derivatives 1a‐j with hydrazine and phenylhydrazine, respectively. The obtained novel indenopyrazoles ( 2a‐j and 3a‐j ) were evaluated for anticancer activity against HeLa and C6 cell lines. Antiproliferative activity was determined by the BrdU proliferation ELISA assay; 2a , 2b , 2d , 2h , and 3h were found to be the most active compounds. The compounds were also screened for antimicrobial activity, and all compounds showed moderate activity against used microorganisms.  相似文献   
992.
In this study, a series of 10 novel copper (II) and silver complexes of 1,3-diaryltriazene-substituted sulfonamides was synthesised. All the synthesised ligands and their metal complexes were assessed for in vitro cytotoxicity against human colorectal adenocarcinoma (DLD-1), cervix carcinoma (HeLa), breast adenocarcinoma (MDA-MB-231), colon adenocarcinoma (HT-29), endometrial adenocarcinoma (ECC-1), prostate cancer (DU-145 and PC-3), normal embryonic kidney (HEK-293), normal prostate epithelium (PNT-1A), and normal retinal pigment epithelium (ARPE-19) cells. Most of the metal complexes from the series showed to be more active against all cancerous cells than the uncomplexed 1,3-diaryltriazene-substituted sulfonamides, and lower cytotoxic effects observed on normal cells. Most of the Cu (II) and Ag (I) metal complexes from the presented series showed high cytotoxic activity against HeLa cells with IC50 values ranging from 2.08 to >300?µM. Specifically, compound L3-Ag showed one of the highest cytotoxicity against all cancer cell lines with IC50 values between 3.30 to 16.18?µM among other tested compounds.  相似文献   
993.
994.
This study reports the length–weight relationships (LWR) of 20 fish species from the Pahang River, Maran district, Pahang, Malaysia. The river supplies fishes mainly for local consumption and is a principal body of water for freshwater aquaculture in Malaysia. A total of 12 LWR of fishes were unknown to FishBase, and five new maximum lengths of fishes were identified from the study.  相似文献   
995.
Four Xanthomonas species are known to cause bacterial spot of tomato and pepper, but the global distribution and genetic diversity of these species are not well understood. A collection of bacterial spot-causing strains from the Americas, Africa, Southeast Asia, and New Zealand were characterized for genetic diversity and phylogenetic relationships using multilocus sequence analysis of six housekeeping genes. By examining strains from different continents, we found unexpected phylogeographic patterns, including the global distribution of a single multilocus haplotype of X. gardneri, possible regional differentiation in X. vesicatoria, and high species diversity on tomato in Africa. In addition, we found evidence of multiple recombination events between X. euvesicatoria and X. perforans. Our results indicate that there have been shifts in the species composition of bacterial spot pathogen populations due to the global spread of dominant genotypes and that recombination between species has generated genetic diversity in these populations.  相似文献   
996.
997.
There is a very little information about the protective effect of lycopene (LYC) against hepatic ischemia–reperfusion injury. The present study was designed to examine the possible protective effect of the strong antioxidant and anti-inflammatory agent, LYC, on hepatic ischemia/reperfusion injury. For this purpose, rats were subjected to 45 min of hepatic ischemia followed by 60 min of reperfusion period. LYC at the doses of 2.5 and 5 mg/kg body weight (bw) were injected intraperitoneally, 60 min prior to ischemia. Upon sacrification, hepatic tissue samples were used for the measurement of catalase (CAT) activity and malondialdehyde (MDA) levels. Also, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were assayed in serum samples. As a result of the use of LYC at the doses of 2.5 and 5 mg/kg bw; while improvements of the ALT, AST, LDH and MDA values were partial and dose-dependent, the improvement of CAT activity was total and dose-independent (p < 0.05). Our findings suggest that LYC has a protective effect against ischemia/reperfusion injury on the liver.  相似文献   
998.
There is an increasing awareness among researchers and others that marginalized and vulnerable groups face problems in accessing health care. Access problems in particular in low-income countries may jeopardize the targets set by the United Nations through the Millennium Development Goals. Thus, identifying barriers for individuals with disability in accessing health services is a research priority. The current study aimed at identifying the magnitude of specific barriers, and to estimate the impact of disability on barriers for accessing health care in general. A population based household survey was carried out in Sudan, Namibia, Malawi, and South Africa, including a total of 9307 individuals. The sampling strategy was a two-stage cluster sampling within selected geographical areas in each country. A listing procedure to identify households with disabled members using the Washington Group six screening question was followed by administering household questionnaires in households with and without disabled members, and questionnaires for individuals with and without disability. The study shows that lack of transport, availability of services, inadequate drugs or equipment, and costs, are the four major barriers for access. The study also showed substantial variation in perceived barriers, reflecting largely socio-economic differences between the participating countries. Urbanity, socio-economic status, and severity of activity limitations are important predictors for barriers, while there is no gender difference. It is suggested that education reduces barriers to health services only to the extent that it reduces poverty. Persons with disability face additional and particular barriers to health services. Addressing these barriers requires an approach to health that stresses equity over equality.  相似文献   
999.
Comprehensive genetic testing has the potential to become the standard of care for individuals with hearing loss. In this study, we investigated the genetic etiology of autosomal recessive nonsyndromic hearing loss (ARNSHL) in a Turkish cohort including individuals with cochlear implant, who had a pedigree suggestive of an autosomal recessive inheritance. A workflow including prescreening of GJB2 and a targeted next generation sequencing panel (Illumına TruSightTM Exome) covering 2761 genes that we briefly called as mendelian exome sequencing was used. This panel includes 102 deafness genes and a number of genes causing Mendelian disorders. Using this approach, we identified causative variants in 21 of 29 families. Three different GJB2 variants were present in seven families. Remaining 14 families had 15 different variants in other known NSHL genes (MYO7A, MYO15A, MARVELD2, TMIE, DFNB31, LOXHD1, GPSM2, TMC1, USH1G, CDH23). Of these variants, eight are novel. Mutation detection rate of our workflow is 72.4%, confirming the usefulness of targeted sequencing approach in NSHL.  相似文献   
1000.

Objective

To develop guidance on what information to include and how to present it in tables summarizing the evidence from systematic reviews of test accuracy following the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

Methods

To design and refine the evidence tables, we used an iterative process based on the analysis of data from four rounds of discussions, feedback and user testing. During the final round, we conducted one-on-one user testing with target end users. We presented a number of alternative formats of evidence tables to participants and obtained information about users’ understanding and preferences.

Results

More than 150 users participated in initial discussions and provided their formal and informal feedback. 20 users completed one-on-one user testing interviews. Almost all participants preferred summarizing the results of systematic reviews of test accuracy in tabular format rather than plain text. Users generally preferred less complex tables but found presenting sensitivity and specificity estimates only as too simplistic. Users found the presentation of test accuracy for several values of prevalence initially confusing but modifying table layout and adding sample clinical scenarios for each prevalence reduced this confusion. Providing information about clinical consequences of testing result was viewed as not feasible for authors of systematic reviews.

Conclusion

We present the current formats for tables presenting test accuracy following the GRADE approach. These tables can be developed using GRADEpro guidelines development tool (www.guidelinedevelopment.org or www.gradepro.org) and are being further developed into electronic interactive tables that will suit the needs of different end users. The formatting of these tables, and how they influence result interpretation and decision-making will be further evaluated in a randomized trial.  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