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   1413298篇
  免费   113379篇
  国内免费   3337篇
耳鼻咽喉   18422篇
儿科学   46618篇
妇产科学   41089篇
基础医学   201074篇
口腔科学   37764篇
临床医学   126167篇
内科学   284930篇
皮肤病学   33438篇
神经病学   117066篇
特种医学   53883篇
外国民族医学   464篇
外科学   210853篇
综合类   32764篇
现状与发展   3篇
一般理论   487篇
预防医学   110168篇
眼科学   31521篇
药学   98628篇
  1篇
中国医学   3353篇
肿瘤学   81321篇
  2021年   10915篇
  2019年   11740篇
  2018年   16659篇
  2017年   12723篇
  2016年   14316篇
  2015年   16062篇
  2014年   22632篇
  2013年   33481篇
  2012年   45516篇
  2011年   48065篇
  2010年   28263篇
  2009年   27135篇
  2008年   44457篇
  2007年   46945篇
  2006年   47509篇
  2005年   45988篇
  2004年   43841篇
  2003年   41799篇
  2002年   40301篇
  2001年   73075篇
  2000年   74612篇
  1999年   61616篇
  1998年   17017篇
  1997年   15450篇
  1996年   15603篇
  1995年   14798篇
  1994年   13399篇
  1993年   12589篇
  1992年   45855篇
  1991年   43508篇
  1990年   41518篇
  1989年   39570篇
  1988年   36204篇
  1987年   35373篇
  1986年   32877篇
  1985年   31290篇
  1984年   23832篇
  1983年   20030篇
  1982年   12208篇
  1981年   10781篇
  1979年   20707篇
  1978年   14581篇
  1977年   12088篇
  1976年   11367篇
  1975年   11622篇
  1974年   13993篇
  1973年   13539篇
  1972年   12645篇
  1971年   11472篇
  1970年   10911篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Pyroglutamyl, proline-rich oligopeptides, classically referred to as bradykinin-potentiating peptides (BPPs) are found in Bothrops jararaca venom, and are naturally occurring inhibitors of the somatic angiotensin-converting enzyme (ACE). The chemical and pharmacological properties of these peptides were essential for the development of captopril, the first active site directed inhibitor of ACE, currently used to treat human hypertension. ACE is a complex ectoenzyme of the vascular endothelium, possessing two catalytic sites, performing diverse specific roles. Recent advances concerning novel features of BPPs revealed that they might still contribute to a better understanding of the cardiovascular physiology and pathology. The molecular biology of the BPPs revealed that they are part of two distinct C-type natriuretic peptide precursors found in the venom gland and the brain of B. jararaca, each containing seven BPPs. In situ hybridization studies detected the presence of the corresponding mRNA precursor in snake brain regions correlated with neuroendocrine functions, such as the ventro-medial hypothalamus, the paraventricular nuclei, the paraventricular organ, and the subcommissural organ. In this article we discuss the large variety of homologous BPPs in B. jararaca venom and brain, its significance, and whether the BPPs could represent novel endogenous neuropeptides.  相似文献   
992.
993.
This study examined race and ethnic differences on the Draw A Person: Screening Procedure for Emotional Disturbance (DAP:SPED; Naglieri, McNeish, & Bardos, 1991) for youths 6 though 17 years of age for 2 matched samples. Samples were drawn from the DAP:SPED nationally representative standardization sample and matched on gender, grade, and school classroom. No statistically significant differences were found for big figure, small figure, or shading item composites. A statistically significant difference was found between Black-White pairs on figure omissions but showed a small effect size (d value = .25). Further, no statistically significant differences were found between the DAP:SPED Total T scores for Black and White youth (M = 47.67, SD = 10.09; N =138) or Hispanic and White youth (M = 48.20, SD = 9.56; N = 59), showing very small effect sizes. In addition, equivalence testing showed similarities across race and ethnic pairs for all composites and DAP:SPED total score, lending preliminary support to the DAP:SPED's clinical utility as a measure that yields similar scores across these groups.  相似文献   
994.
A toxicologic and dermatologic review of cinnamic acid when used as a fragrance ingredient is presented.  相似文献   
995.
Using the indirect immunofluorescent assay, we observed the variation of T-lymphocyte subsets of peripheral blood in 100 patients of primary bronchogenic carcinoma and 31 cases with active pulmonary tuberculosis. Serum CEA were measured simultaneously. The decrease of OKT3+, OKT4+, OKT8+ lymphocytes were significant in patients with lung cancer than that in healthy controls (P less than 0.01). The ratio of OKT4+/OKT8+ increased. It suggested that both cellular immunoincompetence and immunoregulatory abnormality were present in patients with lung cancer. After the resection of tumors 65 cases, the percentage of OKT4+ cells increased at the first week. Fourty seven cases were observed continuously for six months, it was found that OKT8+ cells increased (P less than 0.01). After anticancer chemotherapy, the patients with small cell carcinoma revealed a similar changes too. After operation and chemotherapy, serum CEA level decreased significantly too.  相似文献   
996.
This study was designed to assess the effects of acute nickel chloride administration on behavioral and autonomic thermoregulation in the rat. In one experiment, male rats of the Fischer 344 strain were injected with nickel chloride (IP) at dosages of 0 to 24.0 mg/kg and placed in an environmental chamber maintained at an ambient temperature (Ta) of 10 or 20 degrees C. Colonic temperature was measured 60 min postinjection. Nickel chloride caused a dose-related decrease in colonic temperature, and the hypothermia was accentuated at the cooler Ta. In a second study, rats injected with 0, 6.0, 12.0, or 24.0 mg/kg nickel chloride were placed in a temperature gradient which allowed the rats to select their preferred thermal environment. Nickel chloride at dosages of 12.0 and 24.0 mg/kg caused a significant reduction in the selected Ta. At these dosages the rats were also significantly hypothermic at 60 min postinjection. In a third experiment, whole-body oxygen consumption (i.e., metabolic rate) was measured at Ta's of 10, 20, and 30 degrees C following a 12.0 mg/kg injection of nickel chloride. Nickel chloride caused an initial depression in metabolic rate and hypothermia at Ta's of 10 and 20 degrees C but not at 30 degrees C. In conclusion, (a) nickel chloride affects both behavioral and autonomic control of thermoregulation in the rat and appears to induce a regulated decrease in body temperature and (b) the behavioral thermoregulatory response of the rat is less sensitive to nickel chloride when compared to the mouse.  相似文献   
997.
Tartrate-resistant acid phosphatase activity (TRAPase) is widely used as a cytochemical marker to distinguish osteoclasts from macrophages and other related cell types. The degree of tartrate resistance, however, may depend on which reaction methods, tissues, or species are used. To investigate this further, we have measured the amount of cytochemical reaction product by microdensitometry. We compared osteoclast acid phosphatase (APase) activity in fresh frozen sections of neonatal rat calvaria using two different reaction methods; one is commonly employed for qualitative histochemistry and includes alpha naphthyl phosphate as substrate, simultaneous coupling to the chromagen Fast Garnet, and a 30-minute reaction time (method A). The other may be used to measure enzyme reaction rates in cells in situ and employs conditions suitable for initial velocity kinetics, namely naphthol-ASBI phosphate as substrate, post coupling to Fast Garnet, and a 2-minute reaction time. Although enzyme reaction rates differed greatly between the two methods, significant inhibition of APase activity by tartrate was observed in calvarial osteoclasts (69% and 59% with methods A and B, respectively), osteoblasts, and spleen macrophages. Using method B, mouse calvarial osteoclasts had similar APase activity to that seen in the rat. Tartrate produced little inhibition in these mouse cells, in contrast to the observations made with rat tissue, but murine spleen macrophages were significantly tartrate sensitive (40% inhibition with tartrate). On this basis, conclusions regarding the cell specificity of TRAPase should be treated cautiously.  相似文献   
998.
A prospective randomized study was carried out on a total of 686 patients who underwent vaginal or abdominal hysterectomy. Of these, 338 were given prophylactic cefotetan (2 g) and 348 piperacillin (2 g). Both drugs were administered as i.v. bolus 30 min before operation. Findings confirm the higher risk of infection with abdominal hysterectomy and the advantages of the long half-life cephalosporin, cefotetan.  相似文献   
999.
Steady flattening of the tumor, increasing reflectivity and decreasing vascularity are echographic signs of successful irradiation treatment. The specific example of an irradiated choroidal melanoma shows that the absence of echographic changes by no means excludes tumor destruction. Because of a dense vitreous body hemorrhage, the melanoma could only be evaluated echographically. Since the echogram lacked evidence of regression, the tumor was locally resected 5 months later. Histology, however, revealed an amorphous mass of dead tissue pervaded by intact vessels. Apparently a successfully irradiated melanoma may generate an echo typical of vital melanoma tissue. The authors therefore draw the conclusion that only a steady tumor growth, as substantiated by an echogram, may be considered an unambiguous sign of tumor vitality.  相似文献   
1000.
The term perfusion has varied connotations in different situations. The word perfusion comes from the Latin to pour or diffuse through or over. Myocardial perfusion depends on (a) coronary artery or vessel flow, and (b) myocardial or muscle flow. The factors which determine perfusion at rest and during stress in coronary vessels and within the myocardium are clearly related but not with a predictable linear relationship. In animals there is extensive literature concerning the regulation of coronary flow and perfusion obtained by many sophisticated methods. In contrast, the techniques that are applicable to humans are relatively crude. To date, the clinical data available suggests that the normal control of coronary flow in man and in dogs is fairly similar but that models of pathology in animals bear little relation to the compensatory changes found in the coronary circulation in man. Although the data available is limited and subject to many technical inaccuracies, this article is confined to the assessment of myocardial perfusion in clinical practice.  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