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   33117篇
  免费   2724篇
  国内免费   1423篇
耳鼻咽喉   391篇
儿科学   651篇
妇产科学   579篇
基础医学   4027篇
口腔科学   566篇
临床医学   3604篇
内科学   5616篇
皮肤病学   773篇
神经病学   2151篇
特种医学   1335篇
外国民族医学   13篇
外科学   4140篇
综合类   4062篇
现状与发展   4篇
一般理论   19篇
预防医学   1937篇
眼科学   1154篇
药学   2630篇
  19篇
中国医学   1086篇
肿瘤学   2507篇
  2024年   61篇
  2023年   434篇
  2022年   939篇
  2021年   1397篇
  2020年   1030篇
  2019年   980篇
  2018年   1092篇
  2017年   963篇
  2016年   966篇
  2015年   1262篇
  2014年   1559篇
  2013年   1513篇
  2012年   2308篇
  2011年   2354篇
  2010年   1384篇
  2009年   1165篇
  2008年   1674篇
  2007年   1734篇
  2006年   1664篇
  2005年   1676篇
  2004年   1212篇
  2003年   1040篇
  2002年   933篇
  2001年   795篇
  2000年   812篇
  1999年   792篇
  1998年   523篇
  1997年   449篇
  1996年   382篇
  1995年   373篇
  1994年   319篇
  1993年   242篇
  1992年   324篇
  1991年   317篇
  1990年   303篇
  1989年   282篇
  1988年   253篇
  1987年   230篇
  1986年   231篇
  1985年   182篇
  1984年   119篇
  1983年   92篇
  1982年   69篇
  1981年   74篇
  1979年   77篇
  1978年   60篇
  1977年   66篇
  1974年   66篇
  1973年   60篇
  1972年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Exogenous antigens are generally presented by Class II major histocompatibility (MHC) molecules. When administered with an adjuvant, however, they are capable of inducing a CD8+ T-cell response where antigen recognition is associated with Class I MHC. Accordingly, immunization with soluble ovalbumin (OVA) alone does not activate CD8+ cytotoxic T cells (CTL) but when given in complete Freund's adjuvant (CFA), or in formulations of a number of novel adjuvants, an OVA-specific CD8+ CTL response can be detected. We show in this report that immunization with soluble OVA mixed with heat-killed Mycobacterium vaccae, but not with other common pathogenic and saprophytic mycobacteria, can activate OVA-specific CD8+ CTL. An OVA-specific CTL response is detected when mice are immunized by either the intraperitoneal or intranasal route and their spleen cells are re-stimulated in vitro. Adjuvant activity of heat-killed M. vaccae is present in M. vaccae culture filtrate, in soluble protein components of whole M. vaccae and in the 65 kDa heat-shock protein (hsp) of M. vaccae. Mycobacterium vaccae has previously been shown to have no adverse side-effects in humans. The current results suggest that M. vaccae may be useful as an adjuvant for vaccines and other immunotherapies where CD8+ CTL responses to exogenous proteins are crucial.  相似文献   
82.
The aim of this study was to compare the efficacy of pure follicle stimulating hormone (FSH) with that of FSH/human menopausal gonadotrophin (HMG) combination in downregulated cycles. A total of 357 patients was evaluated retrospectively. Sixty percent of patients in the FSH group and 55% in the FSH/HMG group were new; the others were repeat patients. Ovulation was suppressed with leuprolide acetate in all patients, followed by either FSH (n = 218) or FSH/HMG (n = 119). There was no difference in patients' age, infertility factors, number of ampoules used, length of stimulation, oestradiol levels on day of human chorionic gonadotrophin (HCG) administration, number of oocytes recovered or the number of embryos transferred. Also, nuclear maturity at aspiration and fertilization rates were not different between the two groups. FSH stimulation resulted in a significantly higher percentage of mature oocytes that showed the typical 'mature' morphological characteristics (P < 0.0001). The clinical pregnancy rates per transfer were 40 and 28% in patients stimulated with pure FSH and FSH/HMG respectively (P < 0.05). The significantly higher number of immature oocytes matured in vitro in the FSH/HMG group (P = 0.001) suggests a possible effect on in-vitro maturation, due to luteinizing hormone present in HMG. The difference in mature oocyte quality may be an important determinant in the higher pregnancy rates for the FSH- stimulated patients.   相似文献   
83.
A method for serological diagnosis of Nipah virus (NiV) is described. DNA encoding truncated G protein of NiV was cloned into the pFastBac HT vector, and the fusion protein to His-tag was expressed in insect cells by recombinant baculovirus. The resulting His-G recombinant fusion protein was purified by affinity chromatography and used as the coating antigen for serological testing by indirect enzyme-linked immunosorbant assay (ELISA). When tested against a panel of swine serum samples, the recombinant G protein-based ELISA successfully discriminated all 40 samples previously determined to be serum neutralizing test (SNT) positive from 11 SNT negatives samples. The data show that the recombinant G protein exhibits the antigenic epitopes and conformation necessary for specific antigen-antibody recognition. The main advantage of the recombinant G protein-based NiV ELISA compared to an ELISA using whole virus antigen is the use of a single antigenic protein instead of inactivated whole virus which is required to be prepared under high risk and cost. This test is suitable for routine diagnosis of NiV and also for epidemiological surveys as it allows highly reliable testing of a large number of sera rapidly.  相似文献   
84.
We describe a simple method for computer quantification of eye movement (EM) potentials during REM sleep. This method can be applied by investigators using either period-amplitude (PA) or Fast Fourier Transform (FFT) spectral EEG analysis without special hardware or computer programming. It provides good correlations with visual ratings of EM in baseline sleep and after administration of GABAergic hypnotics. We present baseline data for both PA and FFT measures for 16 normal subjects, studied for 5 consecutive nights. Both visually rated and computer-measured EM density (EMD) showed high night-to-night correlations across baseline and drug nights and the computer measures detected the EMD suppression that is produced by GABAergic drugs. Measurement of EM in addition to stage REM provides biologically significant information and application of this simple computer method, which does not require pattern recognition algorithms or special hardware, could provide reliable data that can be compared across laboratories.  相似文献   
85.
86.
Friedreich's ataxia (FRDA) is the result of mutations in the nuclear-encoded frataxin gene, which is expressed in mitochondria. Several lines of evidence have suggested that frataxin is involved in mitochondrial iron homeostasis. We have transfected the frataxin gene into lymphoblasts of FRDA compound heterozygotes (FRDA-CH) with deficient frataxin expression to produce FRDA-CH-t cells in which message and protein are rescued to near-physiological levels. FRDA-CH cells were more sensitive to oxidative stress by challenge with free iron, hydrogen peroxide and the combination, consistent with a Fenton chemical mechanism of pathophysiology, and this sensitivity was rescued to control levels in FRDA-CH-t cells. Iron challenge caused increased mitochondrial iron levels in FRDA-CH cells, and a decreased mitochondrial membrane potential (MMP), both of which were rescued in FRDA-CH-t cells. The rescue of the low MMP, and high mitochondrial iron concentration by frataxin overexpression suggests that these cellular phenotypes are relevant to the central pathophysiological process in FRDA which is aggravated by exposure to free iron. However, even at physiological iron concentrations, FRDA-CH cells had decreased MMP as well as lower activities of aconitase and ICDH (two enzymes supporting MMP), and twice the level of filtrable mitochondrial iron (but no increase in total mitochondrial iron), and the observed phenotypes were either fully or partially rescued in FRDA-CH-t cells. Free iron is known to be toxic. The observation that frataxin deficiency (either directly or indirectly) causes an increase in filtrable mitochondrial iron provides a new hypothesis for the mechanism of cell death in this disease, and could be a target for therapy.  相似文献   
87.
88.
高师贫困生自我效能感与主观幸福感的特点及关系研究   总被引:2,自引:0,他引:2  
目的分析高师贫困生自我效能感、主观幸福感的特点及关系,为心理健康教育提供依据。方法采用一般自我效能感量表、生活满意度量表、快乐感量表,对218名贫困生和216名非贫困生进行测查。结果①高师贫困生生活满意度、快乐感显著低于非贫困生(t=4.811,P〈0.001;t=2.504,P〈0.05),自我效能感差异不显著。②高师贫困生自我效能感存在性别差异(t=2.117,P〈0.05),男生的自我效能感显著高于女生;生活满意度年级差异显著(F=3.547,P〈0.05),大一学生的生活满意度显著高于大二和大三学生,大二和大三之间的差异不显著。③高师贫困生自我效能感与生活满意度、快乐感呈显著正相关(r=0.349,P〈0.01;r=0.436,P〈0.01)。自我效能感水平越高,幸福感越强。结论高师贫困生主观幸福感相对较低,自我效能感与主观幸福感显著相关,通过提升自我效能感水平可以增强主观幸福感。  相似文献   
89.
Partial androgen insensitivity with sex phenotype variation in two unrelated families was associated with missense mutations in the androgen receptor (AR) gene that disrupted the AR NH(2)-terminal/carboxy terminal interaction. Each mutation caused a single amino acid change within the region of the ligand-binding domain that forms activation function 2 (AF2). In one family, the mutation I737T was in alpha helix 4 and in the other F725L was between helices 3 and 4. Neither mutation altered androgen binding as determined by assays of mutant AR in the patient's cultured genital skin fibroblasts or of recombinant mutant receptors transfected into COS cells. In transient cotransfection assays in CV1 cells, transactivation with the AR mutants at low concentrations of DHT was reduced several fold compared with wild-type AR but increased at higher concentrations. Defects in NH(2)-terminal/carboxy terminal interactions were identified in mammalian two hybrid assays. In similar assays, there was reduced binding of the p160 coactivators TIF2/SRC2 and SRC1 to the mutant AR ligand binding domains (LBD). In the family with AR I737T, sex phenotype varied from severely defective masculinization in the proband to a maternal great uncle whose only manifestation of AIS was severe gynecomastia. He was fertile and passed the mutation to two daughters. The proband of the F725L family was also incompletely masculinized but was raised as a male while his half-sibling by a different father was affected more severely and reared as a female. These studies indicate that the function of an AR AF2 mutant in male development can vary greatly depending on the genetic background.  相似文献   
90.
We have characterized six chemically induced mutations of the Drosophila dlm-defective (d l m d) gene. The mutants are flightless, but they have an otherwise normal appearance. By electron microscopic examination, a focal atrophy was found in their dorsal longitudinal muscle (DLM) fibers, but no abnormalities in nerve conduction or synaptic transmission were detected by electrophysiological tests. The nerve-evoked muscle spike also seemed to be normal, except that the resting potential of DLM in mutant flies was lower and their membrane excitability was higher than those in the wild type flies. The possible causes of the DLM degeneration in this strain are discussed.  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