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   115986篇
  免费   11133篇
  国内免费   9033篇
耳鼻咽喉   983篇
儿科学   1088篇
妇产科学   1151篇
基础医学   13842篇
口腔科学   1940篇
临床医学   15673篇
内科学   17095篇
皮肤病学   1210篇
神经病学   6200篇
特种医学   4270篇
外国民族医学   78篇
外科学   11818篇
综合类   20715篇
现状与发展   40篇
一般理论   6篇
预防医学   7727篇
眼科学   3341篇
药学   12164篇
  94篇
中国医学   7091篇
肿瘤学   9626篇
  2024年   366篇
  2023年   1776篇
  2022年   4314篇
  2021年   6323篇
  2020年   4714篇
  2019年   4003篇
  2018年   4165篇
  2017年   3714篇
  2016年   3552篇
  2015年   5424篇
  2014年   6648篇
  2013年   5855篇
  2012年   8524篇
  2011年   9408篇
  2010年   5927篇
  2009年   4680篇
  2008年   6049篇
  2007年   5984篇
  2006年   5800篇
  2005年   5865篇
  2004年   3815篇
  2003年   3495篇
  2002年   2999篇
  2001年   2657篇
  2000年   2808篇
  1999年   2985篇
  1998年   1985篇
  1997年   2004篇
  1996年   1550篇
  1995年   1472篇
  1994年   1271篇
  1993年   792篇
  1992年   987篇
  1991年   794篇
  1990年   664篇
  1989年   624篇
  1988年   520篇
  1987年   448篇
  1986年   398篇
  1985年   298篇
  1984年   136篇
  1983年   116篇
  1982年   68篇
  1981年   72篇
  1980年   47篇
  1979年   54篇
  1974年   1篇
  1965年   1篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
人TH基因重组腺病毒的构建及生物学活性研究   总被引:2,自引:0,他引:2  
将人酪氨酸羟化酶cDNA表达盒克隆于质粒型腺病毒载体p△Elsp1A,得到重组质粒pAd-TH。随后用脂质体法将重组质粒pAd-TH和拯救型腺病毒质粒pBHG11一起共转染293细胞,通过体内同源重组生成重组腺病毒AdCMVth,THcDNA重组进入腺病毒E1区并受CMV启动子控制。采用形态学、病毒核酸酶切和PCR/RT-PCR等方法进行鉴定正确。重组腺病毒滴度达到1010pfu/ml。初步结果表明,该重组腺病毒感染MN9D细胞后可使细胞内多巴胺水平增加1倍,显示出明显的TH生物学活性。提示TH重组腺病毒AdCMVth可作为高效的基因转移载体用于帕金森氏病基因治疗。  相似文献   
992.
听源性惊厥易感性大鼠上丘神经元构筑的研究   总被引:1,自引:1,他引:1  
用石蜡切片Nissl染色方法,光镜下计数、结合计算机图象分析系统观察、测量惊厥鼠与正常鼠土丘神经元的一些指标.结果显示:(1)在吻例段和中段上丘第Ⅱ层和吻侧段上丘第Ⅲ层的神经元胞体平均直径惊厥鼠显著小于正常鼠,说明惊厥鼠上丘上述部位神经元较小;(2)在吻侧段上丘第Ⅵ层,中段上丘第Ⅰ、Ⅱ层和屋倒段上丘第Ⅴ层,神经元剖面椭圆率惊厥鼠显著地小于正常鼠,说明惊厥鼠土丘上述部位神经元胞体较细长;(3)除第Ⅲ层外,土丘各板层神经元剖面面数密度惊厥鼠都大于正常鼠.本研究结果表明,惊厥鼠的土丘有神经元的形态学变化。这种变化与惊厥鼠惊厥易感性的形成之间是否存在着某种关系,有待深入研究.  相似文献   
993.
Approximately a million bone grafts are performed each year in the United States, and this number is expected to increase rapidly as the population ages. Calcium phosphate cement (CPC) can intimately adapt to the bone cavity and harden to form resorbable hydroxyapatite with excellent osteoconductivity and bone-replacement capability. The objective of this study was to develop a strong CPC using synergistic reinforcement via suture fibers and chitosan, and to determine the fiber strength-CPC composite strength relationship. Biopolymer chitosan and cut suture filaments were randomly mixed into CPC. Both suture filaments and composite were immersed in a physiological solution. After 1-day immersion, cement flexural strengths (mean +/- SD; n = 6) were: (2.7 +/- 0.8) MPa for CPC control; (11.2 +/- 1.0) MPa for CPC-chitosan; (17.7 +/- 4.4) MPa for CPC-fiber composite; and (40.5 +/- 5.8) MPa for CPC-chitosan-fiber composite. They are significantly different from each other (Tukey's at 0.95). The strength increase from chitosan and fiber together in CPC was much more than that from either fiber or chitosan alone. The composite strength became (9.8 +/- 0.6) MPa at 35-day immersion and (4.2 +/- 0.7) MPa at 119 days, comparable to reported strengths for sintered porous hydroxyapatite implants and cancellous bone. After suture fiber dissolution, long macropore channels were formed in CPC suitable for cell migration and tissue ingrowth. A semiempirical relationship between suture fiber strength S(F) and composite strength S(C) were obtained: S(C) = 14.1 + 0.047 S(F), with R = 0.92. In summary, this study achieved substantial synergistic effects by combining random suture filaments and chitosan in CPC. This may help extend the use of the moldable, in situ hardening hydroxyapatite to moderate stress-bearing orthopedic applications. The long macropore channels in CPC should be advantageous for cell infiltration and bone ingrowth than conventional random pores and spherical pores.  相似文献   
994.
Xu J  Rodriguez D  Kim JJ  Brooks PC 《Hybridoma》2000,19(5):375-385
The extracellular matrix (ECM) plays a fundamental role in the regulation of normal and pathological processes. The most abundantly expressed component found in the ECM is collagen. Triple helical collagen is known to be highly resistant to proteolytic cleavage except by members of the matrix metalloproteinase (MMP) family of enzymes. To date little is known concerning the biochemical consequences of collagen metabolism on human diseases. This is due in part to the lack of specific reagents that can distinguish between proteolyzed and triple helical forms of collagen. Here we used the technique of Subtractive Immunization (SI) to generate two unique monoclonal antibodies (MAbs HUIV26 and HUI77) that react with denatured and proteolyzed forms of collagen, but show little if any reaction with triple helical collagen. Importantly, HUIV26 and HUI77 react with cryptic sites within the ECM of human melanoma tumors, demonstrating their utility for immunohistochemical analysis in vivo. Thus, the generation of these novel MAbs not only identify specific cryptic epitopes within triple helical collagen, but also provide important new reagents for studying the roles of collagen remodeling in normal as well as pathological processes.  相似文献   
995.
We have investigated the polymorphism of the DQA1 promoter region (QAP) and we have deduced four point (DRB1, QAP, DQA1, DQB1) haplotypes of 60 unrelated healthy Dai minority individuals using the polymerase chain reaction and Dig-ddUTP labeled oligonucleotides. A total of eight QAP alleles (QAP1.1, 1.2, 1.3, 1.4, 3.1, 3.2, 4.1 and 4.2) were detected and two QAP alleles, QAP1.5 and QAP2.1 were absent in this population. The most predominant allele was QAP1.2 with 80% allele frequency. We also found that QAP alleles are in strong linkage disequilibrium with certain alleles of the neighboring loci DQA1 and DQB1. Complete positive association was found for QAP4.1-DQA1*05, QAP4.2-DQA1*0601, QAP1.2-DR2 group, QAP3.2-DRB1*09, QAP4.1-DRB1*03. A total of 28 different four point (DRB1-QAP-DQA1-DQB1) haplotypes were deduced and the most frequent haplotypes were DRB1*1602-QAP1.2-DQA1*0102-DQB1*0502 (N = 18, H.f. = 15%) and DRB1*09-QAP3.2-DQA1*03-DQB1*03032 (N = 18, H.f. = 15%) followed by the haplotypes DRB1*1401-QAP1.3-DQA1*01-DQB1*0502, DRB1*1202-QAP4.2-DQA1*0601-DQB1*0301 and DRB1*1502-QAP1.2-DQA1*0101-DQB1*0501 with H.f. 9.1%, 6.7% and 5.0% respectively. The other 23 haplotypes were all less than 5% (H.f. 0.8%-5%). The relationship between the QAP alleles and DQA1 in the Dai minority is the same as that in the Chinese and the Caucasoid population.  相似文献   
996.
北京地区精神分裂症患者家属情感表达测查报告   总被引:10,自引:2,他引:10  
目的;探讨北京地区的住院精神分裂症患者家属情感表达方式及测查方法的实用性、测查工具应用的一致性。方法:经过训练的研究人员,采用费氏修订的CFI-CV访谈提纲,对171例住院精神分裂症患者家庭的284位家属进行访谈和录音,并将录音打印成文字资料。  相似文献   
997.
AIM: To evaluate the relationship between IL-18 levels in urine and parameters of renal pathological changes in patients with lupus nephritis (LN). METHODS: IL-18 levels in morning free urine and 24-hour's urine in 19 normal persons and 55 patients with LN were measured by ELISA. The correlation between IL-18 levels and parameters of renal pathological changes, namely activity index (AI) and chronicity index (CI), were analyzed by liner correlation analysis method. RESULTS: IL-18 levels in morning free urine and 24-hour's urine in LN group were elevated significantly compared with control group. In both groups IL-18 levels in morning free urine were (247.1+/-317.5) ng/L and (20.3+/-14.5) ng/L, respectively, P<0.001; those in 24-hour's urine were (192.1+/-170.1) ng/d and (21.0+/-3.8) ng/d, respectively, (P<0.001). There was close positive correlation between IL-18 levels in morning free urine and 24-hour's urine and LN patient's AI (for morning free urine: r=0.602, P<0.001; for 24-hour's urine: r=0.461, P<0.005) but there was no correlation between IL-18 levels in morning urine and 24-hour's urine and CI (P>0.05). Patients with LN were divided into three groups (high, moderate and low) according to AI value. There was distinct difference of IL-18 levels in urine among the three groups: IL-18 levels in morning urine were (69.2+/-82.7) ng/L, (193.5+/-106.1) ng/L and (580.7+/-453.1) ng/L, respectively, (P<0.001); those in 24-hour's urine were (103.5+/-141.4) ng/d, (188.8+/-124.0) ng/d and (333.1+/-183.2) ng/d, respectively. CONCLUSION: It is very simple and convenient to detect IL-18 levels in morning free urine, so it is a good method for evaluating renal pathological activity of LN.  相似文献   
998.
建立慢性酒精中毒致大鼠学习记忆障碍模型,通过免疫组织化学法检测大鼠大脑皮层、海马和丘脑内钙神经素(calci-neurin,CaN)和Tau蛋白Thr231位点(Tau-Thr231)的分布与表达,探讨其在慢性酒精中毒致大鼠学习记忆障碍发病机理中的作用。成年雄性SD大鼠随机平均分为对照组和染毒组。对照组大鼠以生理盐水灌胃,染毒组则以55%酒精灌胃。运用Morris水迷宫检测大鼠学习记忆功能损伤情况,免疫组织化学法检测大脑皮层、海马和丘脑CaN和Tau-Thr231分布及表达,并测定CaN和Tau-Thr231免疫阳性细胞数。慢性酒精中毒后大鼠学习记忆功能有不同程度损伤。染毒组大脑皮层和海马CaN表达较对照组上调(P<0.05);染毒组大脑皮层和海马Tau-Thr231表达较对照组下调(P<0.05)。丘脑未见CaN表达,对照组丘脑可见Tau-Thr231免疫阳性细胞分布,染毒组Tau-Thr231免疫阳性细胞数量逐渐减少,提示慢性酒精中毒致大鼠学习记忆功能损伤可能与大鼠大脑皮层、海马和丘脑内CaN和Tau-Thr231的表达变化相关。  相似文献   
999.
1000.
In this study, a human adult testis cDNA microarray was constructed and hybridized with (33)P-labeled human adult testis, embryo testis and sperm cDNA probes, respectively. A novel alternative splice variant of BRDT gene, named BRDT-NY, presumably involved in testicular function was cloned. It was expressed 3.96-fold more in human adult than embryo testis and also expressed in human spermatozoa. Similarly, RT-PCR revealed a differential expression pattern of this gene in human adult testes and fetal testes. The full length of BRDT-NY was 3438 bp and contained a 2883 bp open reading frame, encoding a 960-amino-acid protein. Sequence analysis showed that it has two bromodomains in N-terminal of the protein. Multiple tissue RT-PCR results showed that BRDT-NY was exclusively expressed in testis. mRNA expression of BRDT-NY gene was deleted in some azoospermic patients' testes. These experiments suggested that BRDT-NY gene may have an important role in the process of spermatogenesis and may be correlated with male infertility.  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