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   89961篇
  免费   8296篇
  国内免费   6577篇
耳鼻咽喉   740篇
儿科学   976篇
妇产科学   1079篇
基础医学   10893篇
口腔科学   1704篇
临床医学   12300篇
内科学   13559篇
皮肤病学   933篇
神经病学   4858篇
特种医学   3373篇
外国民族医学   62篇
外科学   8829篇
综合类   15320篇
现状与发展   60篇
一般理论   3篇
预防医学   5329篇
眼科学   2585篇
药学   9198篇
  70篇
中国医学   4954篇
肿瘤学   8009篇
  2024年   480篇
  2023年   1848篇
  2022年   3898篇
  2021年   4717篇
  2020年   3627篇
  2019年   3116篇
  2018年   3209篇
  2017年   2970篇
  2016年   2684篇
  2015年   4210篇
  2014年   5016篇
  2013年   4274篇
  2012年   6373篇
  2011年   7189篇
  2010年   4369篇
  2009年   3362篇
  2008年   4240篇
  2007年   4561篇
  2006年   4464篇
  2005年   4573篇
  2004年   2820篇
  2003年   2574篇
  2002年   2251篇
  2001年   1932篇
  2000年   2179篇
  1999年   2553篇
  1998年   1721篇
  1997年   1657篇
  1996年   1272篇
  1995年   1098篇
  1994年   922篇
  1993年   641篇
  1992年   722篇
  1991年   620篇
  1990年   562篇
  1989年   501篇
  1988年   416篇
  1987年   368篇
  1986年   252篇
  1985年   201篇
  1984年   96篇
  1983年   80篇
  1982年   49篇
  1981年   55篇
  1980年   41篇
  1979年   32篇
  1978年   5篇
  1976年   13篇
  1975年   10篇
  1974年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
暗柳橙(Citrus sinensis Osbeck)第一次生理落果期(3月下旬~4月中旬)的果实外植体脱落过程中,离区纤维素酶A、B的活性明显升高,第二次落果(4月下旬~5月中旬)期的果实脱落过程中,纤维素酶A的活性也显著提高,但纤维素酶B活性变化较小。细胞内、外纤维素酶的活性在外植体脱落过程中也不断升高。2,4—D能明显抑制胞内、外纤维素酶及纤维素酶A的活性,同时还能抑制外植体及非离休果实内乙烯的产生,但对纤维素酶B活性的影响无明显效应。田间喷布低浓度的2,4—D,明显地减少第一次生理落果,但对第二次落果的作用不如赤霉素。本文还讨论了果实的脱落、纤维素酶活性与乙烯之间的相互关系,及2,4—D的调控作用。并认为采用外植体的方法不失为研究脱落问题的有效手段。  相似文献   
82.
The genetic basis for addiction to tobacco smoking--particularly that of the perception of olfactory stimuli that may be important in reinforcing smoking addiction--is largely unknown. A cluster of genes for olfactory receptors is in close proximity to the MHC region on chromosome 6. Polymorphisms of MHC class III genes (RCCX modules, TNFA promoter polymorphisms) were determined in 101 healthy subjects and 232 coronary artery disease (CAD) patients from Hungary with defined tobacco smoking habits. A highly significant association between ever smoking (past + current smokers) and a specific MHC haplotype was observed (odds ratios = 2.14-4.13; P-values = 0.012 to <0.001). This haplotype is characterized by the presence of C4A null alleles and a solitary short C4B gene linked to the TNF2 allele of the promoter for TNFA gene. This haplotype occurred more frequently in the ever smokers than in the never smokers [odds ratio: 4.97 (1.96-12.62); P = 0.001], and such associations were stronger in women (odds ratio = 13.6) than in men (odds ratio = 2.79). An independent study of complement C4 protein polymorphism and smoking habits in Icelandic subjects (n = 351) yielded similar and confirmative results. Considering the documented link between olfactory stimuli and smoking in females, and the presence of a cluster of odorant receptor genes close to the MHC class I region, our findings implicate a potential role of the MHC-linked olfactory receptor genes in the initiation of smoking.  相似文献   
83.
根据呼气相胸片中肺部区域灰度较高的特点,通过边缘提取和边缘跟踪确定胸部区域,运用最大类间方差方法确定图像分割的阈值.再提取出肺部区域,然后求出肺部的灰度均值。但这样的结果并不理想。于是在此基础上提出修正方案,即以肺部灰度均值和骨骼灰度均值的比值作为特征值.即比例法。此方法可以较客观的识别呼气相胸片。最后用类间距离对这两种方法进行了量化比较。  相似文献   
84.
We review our studies on the role of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in breast cancer. Additionally we report on analyses of the reliability of the scoring procedures used with immunohistochemical assay for PAH-DNA adducts and of potential bias arising from the use of benign breast disease (BBD) controls. We conducted a case-control study utilizing two control groups: BBD controls who donated tissue and blood samples, and healthy controls who donated blood samples. In comparisons of tumor tissue from cases and benign tissue from BBD controls, increasing adduct levels were significantly associated with case-control status [odds ratio (OR) = 2.40, 95% confidence interval (CI) 1.18-4.92], whereas in comparisons of nontumor tissue from cases and benign tissue from BBD controls the association was nonsignificant (OR = 1.97, 95% CI 0.94-4.17). We also show among cases, but not among BBD controls, that the GSTM1 null genotype is associated with increased adduct levels in breast tissue. Our reliability study found the scoring procedures used with the immunohistochemical assay to have high reliability, 0.93 in nontumor, 0.82 in tumor, and 0.74 in benign tissues. However, we found that the technician significantly contributed to the total variability of a series of data. Finally, we did not find a consistent bias to the null associated with the use of BBD controls; however, BBD controls may overestimate the prevalence of family history of breast cancer compared to that of healthy controls (18% vs.14%). We hypothesize that the higher prevalence results from a referral bias and discuss how this may influence our results.  相似文献   
85.
LJM, a 41-year-old schizophrenic Chinese man with bilateral anterior cingulate gyrus (Brodmann's area 24) lesions and also a small lesion in right amygdala after an operation, was compared with normal as well as brain-damaged and schizophrenic controls in identification of morphed facial expressions of six basic emotions. In repeated administrations of the test for recognition of facial emotions, over a 1- year period, LJM performed significantly worse for expressions of fear compared with the three groups of controls. Recognition of other emotions was not significantly different from that of the controls, except that his recognition of disgust during the first session (but not in two subsequent sessions) was worse than normal and brain-damaged controls but not worse than schizophrenic controls. The dissociation between recognition of fear and other emotions supported the view that the brain has separable networks for processing different emotions, and that the right amygdala as well as the anterior part of bilateral cingulate gyrus are possible substrates involved in the special network for perception of fear. The results from the various groups of Chinese subjects indicate that they perceive emotions in a categorical manner, and that the six basic emotions are likely to be cross-cultural universals.  相似文献   
86.
Alport's syndrome is characterized clinically by a nonimmune glomerulopathy, often accompanied by sensorineural hearing loss and lens abnormalities, frequently due to mutations in the COL4A5 gene. The association of AS with diffuse leiomyomatosis, a benign proliferation of smooth muscle that occurs most often in the esophagus, trachea, and female genitalia, has been reported. Recently, a deletion involving both the COL4A5 and COL4A6 genes has been reported in four unrelated families. We report an additional case with Alport's syndrome associated with leiomyomatosis carrying a deletion of both COL4A5 and COL4A6 genes. A detailed characterization of the genomic region involved in the deletion event has been performed. Our results demonstrate that the deletion removed exon l of COL4A5 and exons l and 2 of COL4A6. © 1994 Wiley-Liss, Inc.  相似文献   
87.
88.
89.
脐带血清对骨髓粒—巨噬细胞集落形成的影响   总被引:1,自引:0,他引:1  
在骨髓细胞半固体琼脂培养体系中,研究脐带血清(CBs)对骨髓粒—巨噬细胞集落形成单位(CFU-GM)的影响,单纯应用CBs培养可使骨髓CFU-GM(x±s为26.0375±10.2327)显著的高于正常成人外周血清(PBs)组(x±s为11.5917±3.6047;P<0.001)。CBs加粒-巨噬细胞刺激因子,GM-CSF组CFU-GM(x±s为119.0792±35.0991)是单纯CBs组的4.57倍;而PBs加GMC-SF组(x±s为97.125±26.7559)是单纯PBs组的8.38倍。有白细胞介素-6(IL-6)存在的CBs组,CFU-GM(x±s为31.9333±10.9144)明显的高于单纯CBs组(P<0.02)。提示CBs中含有较高水平的内源性GM-CSF。  相似文献   
90.
We report that gp49B1, a mast cell membrane receptor with two immunoreceptor tyrosine-based inhibitory motifs (ITIM), constitutively inhibits mast cell activation-secretion induced by stem cell factor (SCF), a tissue-derived cytokine that also regulates mast cell development. The intradermal injection of SCF into the ears of gp49B1 null (gp49B(-/-)) mice elicited approximately 4- and 2.5-fold more degranulating mast cells and tissue swelling caused by edema, respectively, than in gp49B(+/+) mice. SCF did not induce tissue swelling in mast cell-deficient mice, and the responsiveness of gp49B(-/-) mice to mast cell-associated amine and lipid mediators was unaltered. When gp49B(+/+) and gp49B(-/-) mice were pretreated with antagonists of the amines, SCF-induced tissue swelling was reduced by >90% and 60%, respectively, and it was reduced by >90% in both genotypes when a cysteinyl leukotriene receptor antagonist was also provided. Hence, the dominant contribution of secretory granule amines to SCF-induced tissue swelling is the result of gp49B1-mediated inhibition of the production of cysteinyl leukotrienes by mast cells. Our findings also provide the first example of an ITIM-bearing receptor that constitutively suppresses inflammation generated in vivo independently of the adaptive immune response by a receptor that signals through intrinsic tyrosine kinase activity rather than immunoreceptor tyrosine-based activation motifs.  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