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   31740篇
  免费   3036篇
  国内免费   76篇
耳鼻咽喉   241篇
儿科学   943篇
妇产科学   831篇
基础医学   5263篇
口腔科学   468篇
临床医学   3658篇
内科学   6180篇
皮肤病学   553篇
神经病学   3072篇
特种医学   1111篇
外科学   3801篇
综合类   396篇
一般理论   30篇
预防医学   3385篇
眼科学   524篇
药学   2110篇
中国医学   43篇
肿瘤学   2243篇
  2023年   273篇
  2022年   506篇
  2021年   1036篇
  2020年   628篇
  2019年   907篇
  2018年   960篇
  2017年   752篇
  2016年   804篇
  2015年   874篇
  2014年   1138篇
  2013年   1581篇
  2012年   2238篇
  2011年   2263篇
  2010年   1152篇
  2009年   1041篇
  2008年   1799篇
  2007年   1784篇
  2006年   1672篇
  2005年   1591篇
  2004年   1486篇
  2003年   1325篇
  2002年   1174篇
  2001年   538篇
  2000年   480篇
  1999年   501篇
  1998年   298篇
  1997年   255篇
  1996年   234篇
  1995年   239篇
  1994年   205篇
  1993年   200篇
  1992年   370篇
  1991年   369篇
  1990年   302篇
  1989年   312篇
  1988年   259篇
  1987年   293篇
  1986年   271篇
  1985年   292篇
  1984年   241篇
  1983年   194篇
  1982年   153篇
  1981年   132篇
  1980年   111篇
  1979年   167篇
  1978年   132篇
  1977年   109篇
  1976年   105篇
  1974年   116篇
  1973年   113篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We retrospectively evaluated 401 selected patients who had estrogen receptor (ER) assays both at primary surgery and at relapse in an accessible site to determine the clinical relevance of the subsequent ER determination. The median time between ER assessments was 27 months (range: 2-122 months). The median follow-up time from diagnosis was 6 years (range: 2-12 years). For patients with ER+ tumors at primary diagnosis, 29% (76/261) had ER- tumors at relapse, while for ER- primaries, the conversion rate was 33% (46/140). Conversions from ER+ to ER- occurred more often when the time interval between assays was less than one year (p = 0.004), while conversions from ER- to ER+ tended to occur late (beyond three years; p = 0.0003). Treatments received between assays (usually adjuvant therapy) had only a slight influence on ER status conversion. Post-relapse survival was poor for patients who had the biopsy accessible recurrence within one year; an expression of the aggressive nature of the disease. Among patients whose accessible relapse was beyond one year, those with ER- primaries who converted to ER+ had a longer survival than those whose recurrence was classified again as ER- (p = 0.006). This group of patients with ER- primaries who recurred beyond one year with an ER+ tumor in an accessible site represented 29% (40/140) of all patients with ER- primaries and had an estimated overall survival rate of more than 60% at 6 years from the accessible relapse. ER determination upon relapse within one year has very little clinical relevance.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
92.
OBJECTIVE: This article examines the success of mini-dental implants (MDI'S) by assessing four subjective measures of patient satisfaction for MDI's in the edentulous maxilla and mandible: comfort, retention, chewing ability and speaking ability. Success rates, surgical techniques, and financial advantages of the MDI's are reviewed. STUDY DESIGN: Thirty consecutive patients received four MDI's between the mental foramen of the mandible from 9/18/2003 to 10/22/2004. Questionnaires were sent to all thirty patients an average of 5 months postoperatively. The patients ranked comfort, retention, chewing ability, and speaking ability from 1 to 10 (1=poor and 10=excellent). RESULTS: A total of 116 MDI's were placed in 13 months and 113 remain stable for a 97.4% implant success rate. Pre-operatively patients rated their retention at 1.7+/-0.42 and post-operatively at 9.6+/-0.37, for a difference of 7.9 (p=3.6-19). Comfort was the next greatest improvement, with a pre-operative rating of 2.2+/-0.63 and a post-operative rating of 9.4+/-0.45, for a difference of 7.2 (p=3.5-15). Chewing ability also improved, with a difference of 7.0 (p=2.9e-16). In the final category of speaking ability, the pre-operative to post-operative difference was 3.2 (p=1.1e-5). CONCLUSION: MDI's are a highly successful implant option for patients with poor tolerance to maxillary and mandibular prosthesis. The implants are relatively affordable and overall patient satisfaction is excellent.  相似文献   
93.
The predominant shapes of small opacities on the chest radiographs of 895 British coalminers have been studied. The aims were to determine whether irregular (as distinct from rounded) small opacities can be identified reproducibly, whether their occurrence is related to dust exposure, and whether they are associated with excess prevalence of respiratory symptoms or impairments of lung function. Six of the doctors responsible for regular radiological surveys of all British coalminers each classified all 895 radiographs twice and independently, using the International Labour Organisation's 1980 classification system. The majority view was that 39 films showed predominantly irregular small opacities, 131 showed predominantly small rounded opacities, and 587 showed no small opacities. Readers' opinions varied about the presence and shapes of shadows on the other 138 films. In general, consistency between readers (and within readers on repeated viewings) was satisfactory. The occurrence and profusion of irregular shadows were related significantly both to the men's ages and additionally to their cumulative exposure to respirable coalmine dust as determined from 15 years' dust monitoring close to where the miners had worked. For any given level of exposure, the average level of profusion of the small irregular opacities was less than the corresponding profusion of small rounded opacities. The prevalence rates of chronic cough and phlegm, and of breathlessness, were higher in those with small irregular opacities than in those with no small opacities (category 0/0), but the differences were not statistically significant after adjustment for other factors including smoking habits. The presence of irregular (but not rounded) small shadows was associated with an impairment in respiratory function averaging about 190 ml deficits in both FEV1 and FVC. These deficits were not explicable in terms of the men's ages, body sizes, and smoking habits and they were in addition to the lung function losses attributable to the miners' dust exposure as such. It is concluded that the presence and profusion of small irregular opacities should be taken into consideration when assessing the severity of coalworkers' simple pneumoconiosis.  相似文献   
94.
95.
Certified Reference Material 470 (CRM 470) demonstrates commutability with both the manufacturer's calibrator and with dilutions of serum pools in the Dade Behring N High Sensitivity assay for C-reactive protein (CRP). Both regression and back calibration show similar nonlinearity for all materials, largely due to the method of calibration curve fitting used in this assay. Significant differences in values among the currently available commercial assays can be largely overcome by using appropriate calibration curve fitting and the recommended value transfer protocol, which includes a minimum of two assay runs on each of at least 3 separate days, with weight correction of all reconstitutions and dilutions. An initial weight-corrected dilution should be made each day because of the relatively high level of CRP in CRM 470. In our opinion, the degree of nonlinearity, imprecision, and differences in values in currently available assays renders the use of fixed clinical decision cut-points questionable for high-sensitivity CRP. An alternative approach is suggested.  相似文献   
96.
Engineering of a variety of rodent tumour cells to secrete either interleukin 2 (IL-2), or interleukin 4 (IL-4), has been demonstrated to reduce their tumorigenicity. However the mechanisms of action of secreted IL-2 and IL-4 have not been compared in a single rodent tumour. Here we demonstrate that the weakly immunogenic murine fibrosarcoma FS29 had reduced growth rate and in some cases was rejected by syngeneic animals, when modified to secrete either IL-2 or IL-4, but not IL-5. Immunohistochemical analysis of tumour nodules undergoing regression showed stimulation of a largely lymphocytic infiltrate by IL-2 and a macrophage and granulocyte infiltrate, with a small number of lymphocytes by IL-4. Indeed, secretion of low levels of IL-2 and IL-4 in combination resulted in optimal rejection, suggesting that the two cytokines might mobilise different and complementary effector cell mechanisms. Both IL-2 and IL-4-secreting cells failed to induce the rejection of admixed, unmodified FS29 cells. The loss of cytokine secreting cells from such admixtures occurred more rapidly for IL-2-secreting cells. Injection of IL-4-secreting, but not IL-2-secreting FS29 cells could protect mice from a delayed challenge with unmodified FS29 cells. These data suggest that IL-4 secretion stimulates the better long-term host anti-tumour response.  相似文献   
97.
Vinylogous hydroxamic acids (3-(N-hydroxy-N-alkylamino)-2-propen-1-ones, VHA) were prepared as antiinflammatory agents. The synthesis, chemical properties, and in vitro biological activities of these relatively unexplored compounds are described. The VHAs were prepared by condensation of the appropriate N-substituted hydroxylamine with any of the three reagents: a 1,3-dicarbonyl compound (method A); a vinylogous amide (method B); or an alkynone (method C). The VHAs exist as one or more tautomers in solution with the relative proportions of each being dependent upon the structure of the VHA, solvent, and pH. VHAs undergo some of the typical reactions of hydroxamic acids as well as those of vinylogous amides. VHAs are active as inhibitors of 5-lipoxygenase and of IL-1 biosynthesis in vitro, which do not inhibit other enzymes of the arachidonic acid cascade. They have been shown by ESR studies to bring about inhibition of soybean type 1 15-lipoxygenase by reduction of the active site iron.  相似文献   
98.
99.
In this study we wanted to investigate the post-operative astigmatism and visual acuity after phacoemulsification and conventional extracapsular cataract surgery. Patients operated between April and June 1993 (n=150) were retrospectively analyzed. The patients were examined prior to surgery and at day 1, at day 10, and in week 6 post-operatively. The difference between the post-operative log mean visual acuity in the Phaco group and in the CECCE group was significant after 1 and 10 days, however it was not significant (p=0.191) after 6 weeks. The mean astigmatism was significantly less in the Phaco group than in the CECCE group during the whole post-operative check-up period. This study suggests that Phaco results in a lower post-operative astigmatism and an earlier visual rehabilitation compared to the CECCE technique.Abbreviations Phaco Phacoemulsification - CECCE Conventional extracapsular cataract extraction  相似文献   
100.
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