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   8074篇
  免费   544篇
  国内免费   24篇
耳鼻咽喉   116篇
儿科学   144篇
妇产科学   141篇
基础医学   1131篇
口腔科学   310篇
临床医学   760篇
内科学   1701篇
皮肤病学   119篇
神经病学   971篇
特种医学   348篇
外科学   1293篇
综合类   63篇
预防医学   440篇
眼科学   90篇
药学   493篇
中国医学   10篇
肿瘤学   512篇
  2023年   38篇
  2022年   87篇
  2021年   145篇
  2020年   114篇
  2019年   164篇
  2018年   164篇
  2017年   121篇
  2016年   139篇
  2015年   173篇
  2014年   213篇
  2013年   286篇
  2012年   448篇
  2011年   517篇
  2010年   281篇
  2009年   285篇
  2008年   434篇
  2007年   455篇
  2006年   472篇
  2005年   443篇
  2004年   371篇
  2003年   387篇
  2002年   335篇
  2001年   179篇
  2000年   187篇
  1999年   172篇
  1998年   104篇
  1997年   95篇
  1996年   83篇
  1995年   52篇
  1994年   40篇
  1993年   51篇
  1992年   132篇
  1991年   105篇
  1990年   104篇
  1989年   99篇
  1988年   111篇
  1987年   110篇
  1986年   80篇
  1985年   82篇
  1984年   64篇
  1983年   51篇
  1982年   37篇
  1981年   36篇
  1979年   52篇
  1977年   33篇
  1976年   37篇
  1975年   40篇
  1974年   46篇
  1973年   41篇
  1971年   42篇
排序方式: 共有8642条查询结果,搜索用时 296 毫秒
71.
Regional cerebral blood flow was measured with positron emission tomography (PET) in six healthy volunteers at rest and during experimentally induced, sustained cutaneous pain on the dorsum of the right hand or on the dorsum of the right foot. Pain was inflicted by intracutaneous injection of capsaicin, providing a mainly C-fibre nociceptive stimulus. Statistical analysis showed significant activations along the central sulcus (SI) area when comparing pain in the hand to pain in the foot. Separate comparison of both pain states to a baseline revealed different locations along the central sulcus for hand pain and foot pain. The encountered differences are consistent with what is previously known about the somatotopics of non-painful stimuli. When comparing painful stimuli to baseline, the contralateral anterior cingulate gyrus, the ipsilateral anterior insular cortex and the ipsilateral prefrontal cortex were implicated. The results are consistent with an involvement of SI in the spatial discrimination of acute cutaneous pain. Received: 17 October 1996 / Accepted: 12 May 1997  相似文献   
72.
By polyacrylamide gel electrophoresis, Duck/Mississippi/75 virus was shown to contain five different types of polypeptides of mol. wt. ranging from 76 X 1O(3) to 43 X 10(3), two of which were glycosylated (mol. wt. 76 X 10(3) and 57 X 10(3). A comparison of this data with similar results obtained using Yucaipa and Newcastle disease virus (NDV) revealed a similarity with NDV, concerning the number, position and mol. wt. of the polypeptides. Haemagglutinating and neuraminidase properties are associated with surface glycoproteins which represent at least 40% of the virus protein. After KCl and Triton X-100 treatment and centrifugation on linear sucrose density gradients (10 to 25%, w/w) it was possible to isolate glycoprotein VP1 of mol. wt 76 X 10(3) with which haemagglutinating and neuraminidase activities were associated.  相似文献   
73.
The emigratory behavior and locomotor activity of yellow-eyed (y/y), wildtype (+/+), and heterozygous (+/y) house flies was examined at 8 fc (86 lx) and 1600 fc (17,223 lx) light intenstities. At 8 fc, emigration rate and activity of the y/y flies was similar to that of the +/+ and +/y flies. However, at 1600 fc, the y/y flies emigrated at twice the rate and showed an activity of about one-third that of the other genotypes. The behavior of the +/+ and +/y flies remained similar regardless of the experimental design or light intensity. The excessive neural stimulation by high-intensity light resulting from reduced shielding pigments led to behavioral modifications in the visual and tactile responses of the y/y flies.This research was supported in part by grants from the CUNY Faculty Research Award Program (No. 1103) and NIH Biomedical Research Support Grant 5-S05-R-07064.  相似文献   
74.
BACKGROUND: The present study was designed to develop a briefer screening scale of approximately 10 items which maintained the validity of the Zung Self-Rating Depression Scale in a sample similar to that attending National Depression Screening Day (NDSD), as well as a more general audience. METHODS: We first administered 70 items from a variety of existing rating scales to 40 subjects who answered an ad for depressed subjects and 55 who answered an ad for non-depressed subjects, all of whose diagnoses were confirmed by the Structured Clinical Interview for DSM-IV (SCID). Based on the correlation between each item and the diagnostic criterion, we reduced the number of items to 17 which we then administered to another 45 subjects who answered an ad similar to that used for NDSD and also underwent a SCID interview. Based on these results, we arrived at the final 10-item Harvard Department of Psychiatry/NDSD scale (HANDS) with the assistance of the item-response theory. The items are scored for frequency of occurrence of each symptom over the past 2 weeks. Total scores range from 0 to 30. RESULTS: The 10-item scale (HANDS) has good internal consistency and validity: a cutpoint score of 9 or greater gave sensitivity of at least 95% in both studies. Although specificity was lower for all scales in the self-selected population, the HANDS performed at least as well as the 20-item Zung Scale, the 21-item Beck Depression Inventory-II and the 15-item Hopkins Symptom Depression Checklist. CONCLUSION: The 10-item HANDS performs as well as other widely used longer self-report scales and has the advantage of briefer administration time.  相似文献   
75.
Language fMRI abnormalities associated with FOXP2 gene mutation   总被引:8,自引:0,他引:8  
Half the members of the KE family suffer from a speech and language disorder caused by a mutation in the FOXP2 gene. We examined functional brain abnormalities associated with this mutation using two fMRI language experiments, one involving covert (silent) verb generation and the other overt (spoken) verb generation and word repetition. The unaffected family members showed a typical left-dominant distribution of activation involving Broca's area in the generation tasks and a more bilateral distribution in the repetition task, whereas the affected members showed a more posterior and more extensively bilateral pattern of activation in all tasks. Consistent with previously reported bilateral morphological abnormalities, the affected members showed significant underactivation relative to the unaffected members in Broca's area and its right homolog, as well as in other cortical language-related regions and in the putamen. Our findings suggest that the FOXP2 gene is critically involved in the development of the neural systems that mediate speech and language.  相似文献   
76.
The erythrocyte sedimentation rate in congestive heart failure   总被引:1,自引:0,他引:1  
BACKGROUND AND METHODS. Physicians have long believed that the erythrocyte sedimentation rate is low in patients with congestive heart failure, but this concept is based on a misinterpretation of the results in a single report published in 1936. To reevaluate this concept in the modern era, we measured the sedimentation rate in 242 patients who were referred for treatment of chronic heart failure. RESULTS. The sedimentation rate was low (less than 5 mm per hour) in only 24 patients (10 percent) but was increased (above 25 mm per hour) in 50 percent. Patients with low or normal sedimentation rates (less than or equal to 25 mm per hour) had more severe hemodynamic abnormalities than patients with elevated rates: lower cardiac index (mean +/- SEM, 1.7 +/- 0.1 vs. 2.0 +/- 0.1 liters per minute per square meter of body-surface area) and higher mean right atrial pressure (mean +/- SEM, 12 +/- 1 vs. 9 +/- 1 mm Hg) (both P less than 0.0001). New York Heart Association functional class IV symptoms were present in 66 percent of the patients with a low or normal sedimentation rate, as compared with 42 percent of those with elevated rates (P less than 0.0001). After one to three months of therapy, patients whose sedimentation rates decreased showed little hemodynamic or clinical response to treatment, whereas both cardiac performance and functional status improved in patients whose rates increased (P less than 0.02 for the comparison between groups). The sedimentation rate was correlated with the plasma fibrinogen level (r = 0.64, P = 0.0025), and changes in the sedimentation rate during treatment were correlated inversely with changes in mean right atrial pressure (r = -0.57, P = 0.0002). During long-term follow-up, patients with low or normal sedimentation rates had a worse one-year survival than patients with elevated rates (41 vs. 66 percent, P = 0.01). CONCLUSIONS. These data indicate that the erythrocyte sedimentation rate is correlated with the severity of illness in patients with chronic heart failure. Because of its lack of discriminatory power, however, the test is of limited value in the clinical management of this disorder.  相似文献   
77.
Mechanisms regulating the content of the putative peptide transmitters, substance P and somatostatin, were examined in several neuronal populations in culture. Substance P levels increased more than 25-fold within 48 h in sympathetic neurons in the explanted rat superior cervical ganglion, and remained elevated for 4 weeks. Identity of the peptide was authenticated by combined high pressure liquid chromatography-radioimmunoassay. Veratridine prevented the increase of substance P in vitro, and tetrodotoxin blocked the veratridine effect, suggesting that sodium ion influx and membrane depolarization prevent peptide elevation. Veratridine (or potassium)-induced membrane depolarization released substance P into the culture medium through a calcium-dependent process. Consequently, at least some veratridine effects are attributable to release and subsequent depletion of ganglion peptide. However, the inhibitory effects of veratridine were far greater than could be accounted for by the quantity of peptide released, suggesting a separate influence on net synthesis (synthesis less catabolism) of substance P. Viewed in conjunction with previous in vivo studies, our observations suggest that trans-synaptic impulses, through the mediation of postsynaptic sodium flux, release substance P from sympathetic neurons and also regulate intracellular peptide metabolism. To determine whether the processes regulating substance P in sympathetic neurons reflect generalized mechanisms, a different peptide, somatostatin, was examined in sympathetic neurons; moreover, substance P was examined in a different neuronal population, special sensory neurons in the nodose ganglion. Substance P levels increased significantly in both sympathetic and sensory neurons after explantation, and somatostatin levels increased in sympathetic neurons. In each instance, the increase was dependent upon the presence of the calcium ions. Moreover, these increases were all prevented by veratridine, in a tetrodotoxin-sensitive manner. Our observations suggest that common regulatory mechanisms govern peptide transmitter metabolism in diverse neuronal populations.  相似文献   
78.
The present study is based on the initiative for quality assurance in pathology of the German Society of Pathology and the Professional Association of German Pathologists. Four panel laboratories with experience and expertise in polymerase chain reaction (PCR) detection of Mycobacterium tuberculosis were selected to establish the prerequisites for continuous external laboratory trials, in particular, by providing pre-tested specimens and evaluation criteria for participating institutes. In the first step, the four panel laboratories performed an internal trial to test their own reliability and reproducibility. Paraffin sections and DNA preparations from 34 tissues (25 clinical specimens and 9 controls) totalling to 66 samples were evaluated by each panel institute according to their own protocols. The methodologies differed and are described in detail. Despite these differences, a high degree of inter-laboratory reliability was achieved. In this report, we summarise our results including the correlation with the histology and provide recommendations for applying PCR-based methodology for the detection of mycobacterial DNA in surgical specimens. Supplementary data are available online at (rubric Forschung). Pre-tested specimens are now available for the external trial and can be ordered from the steering institute via Oligene (). All molecular pathology laboratories are invited to participate in this quality assurance initiative.  相似文献   
79.
80.
Differential effects of growth factors on tissue-engineered cartilage   总被引:18,自引:0,他引:18  
The effects of four regulatory factors on tissue-engineered cartilage were examined with specific focus on the ability to increase construct growth rate and concentrations of glycosaminoglycans (GAG) and collagen, the major extracellular matrix (ECM) components. Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid (PGA) scaffolds and cultured in medium with or without supplemental insulin-like growth factor (IGF-I), interleukin-4 (IL-4), transforming growth factor-beta1 (TGF-beta1) or platelet-derived growth factor (PDGF). IGF-I, IL-4, and TGF-beta1 increased construct wet weights by 1.5-2.9-fold over 4 weeks of culture and increased amounts of cartilaginous ECM components. IGF-I (10-300 ng/mL) maintained wet weight fractions of GAG in constructs seeded at high cell density and increased by up to fivefold GAG fractions in constructs seeded at lower cell density. TGF-beta1 (30 ng/mL) increased wet weight fractions of total collagen by up to 1.4-fold while maintaining a high fraction of type II collagen (79 plus minus 11% of the total collagen). IL-4 (1-100 ng/mL) minimized the thickness of the GAG-depleted region at the construct surfaces. PDGF (1-100 ng/mL) decreased construct growth rate and ECM fractions. Different regulatory factors thus elicit significantly different chondrogenic responses and can be used to selectively control the growth rate and improve the composition of engineered cartilage.  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