全文获取类型
收费全文 | 252083篇 |
免费 | 17865篇 |
国内免费 | 1139篇 |
专业分类
耳鼻咽喉 | 2787篇 |
儿科学 | 6513篇 |
妇产科学 | 4599篇 |
基础医学 | 32954篇 |
口腔科学 | 4558篇 |
临床医学 | 25329篇 |
内科学 | 53621篇 |
皮肤病学 | 3383篇 |
神经病学 | 24282篇 |
特种医学 | 8400篇 |
外国民族医学 | 11篇 |
外科学 | 38494篇 |
综合类 | 3456篇 |
一般理论 | 318篇 |
预防医学 | 21401篇 |
眼科学 | 6559篇 |
药学 | 16967篇 |
6篇 | |
中国医学 | 361篇 |
肿瘤学 | 17088篇 |
出版年
2023年 | 1341篇 |
2022年 | 2411篇 |
2021年 | 5439篇 |
2020年 | 3262篇 |
2019年 | 5300篇 |
2018年 | 5952篇 |
2017年 | 4470篇 |
2016年 | 4959篇 |
2015年 | 5830篇 |
2014年 | 8605篇 |
2013年 | 11794篇 |
2012年 | 18012篇 |
2011年 | 18898篇 |
2010年 | 10575篇 |
2009年 | 9430篇 |
2008年 | 16597篇 |
2007年 | 17455篇 |
2006年 | 17304篇 |
2005年 | 17281篇 |
2004年 | 16194篇 |
2003年 | 15043篇 |
2002年 | 14060篇 |
2001年 | 2113篇 |
2000年 | 1614篇 |
1999年 | 2322篇 |
1998年 | 3065篇 |
1997年 | 2563篇 |
1996年 | 2187篇 |
1995年 | 2096篇 |
1994年 | 1744篇 |
1993年 | 1572篇 |
1992年 | 1260篇 |
1991年 | 1154篇 |
1990年 | 1005篇 |
1989年 | 973篇 |
1988年 | 968篇 |
1987年 | 945篇 |
1986年 | 951篇 |
1985年 | 965篇 |
1984年 | 1217篇 |
1983年 | 1123篇 |
1982年 | 1365篇 |
1981年 | 1312篇 |
1980年 | 1145篇 |
1979年 | 703篇 |
1978年 | 747篇 |
1977年 | 635篇 |
1976年 | 584篇 |
1975年 | 469篇 |
1974年 | 472篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Poly(propylene)s with narrow molecular weight distributions were prepared with various methylaluminoxane-activated metallocene-based Ziegler-Natta catalysts to study the influence of randomly incorporated regio- and stereoirregularities on the crystallization behavior. As a function of the metallocene type and the polymerization temperature, the molecular weights varied between 11500 < M n < 63 000, melting temperatures of annealed samples between 125 to 158°C, and the corresponding degrees of crystallinity, as measured by wide-angle X-ray scattering, between 49 and 67%. While the virgin poly(propylene)s exhibited exclusively the α-modification, annealing and melt crystallization favored the development of the γ-modification. The microstructure analysis by 13C NMR spectroscopy revealed a linear correlation between the content of the γ-modification and the average length of the isotactic segments. 相似文献
992.
Venom from young (0 to 48 hours after eclosion) Vespa orientalis should presumably be less allergenic and/or antigenic than venom from adult hornets. This point was confirmed by skin tests, by crossed immunoelectrophoresis and by radioallergosorbent test (RAST), using rabbit IgG antibodies and human IgE antibodies. It is suggested that the venom of young hornets could have therapeutic applications. 相似文献
993.
Richard J. Davidson Mark E. Horowitz Gary E. Schwartz David M. Goodman 《Psychophysiology》1981,18(1):36-41
Based upon suggestions that the two cerebral hemispheres may be differentially involved in the perception and regulation of autonomic activity, three studies were designed to explore differences in the relationship between left versus right hand finger tapping and the heartbeat. In each study, right-handed subjects were asked to tap with either their left versus right forefingers regularly at the rate of approximately once per second. When the time from the R-spike immediately preceding their tap to the tap was examined, a significant difference between the two hands was obtained in two of the studies, with the left hand tapping closer to the last R-spike compared with the right. A variety of additional conditions in the experiments suggest that this effect may depend upon tapping rhythmically. The implications of these findings for the differential role of the left and right hemispheres in the perception and regulation of cardiac activity are considered. 相似文献
994.
Turner CK Blieden TM Smith TJ Feldon SE Foster DC Sime PJ Phipps RP 《Journal of immunological methods》2004,291(1-2):63-70
The purpose of this study was to develop an enzyme-linked immunospot assay (ELISpot assay) that can be used with human adherent cells. While standard enzyme-linked immunosorbent assays (ELISAs) are available and widely used and ELISpot assays are used for nonadherent lymphocytes, no ELISpot assay has been developed for adherent cells. We used primary human fibroblasts from four different tissues (myometrium, lung, gingiva, and orbit), either unstimulated or interleukin (IL)-1beta-activated, to evaluate an ELISpot assay. Antibody pairs for IL-6 and IL-8 were used and results were compared to a standard ELISA. We found that we could reliably detect IL-6 and IL-8 spots with as few as 10 fibroblasts. Optimal cell numbers were 50 cells per well incubated for 8 h, although spots appeared as early as 2 h after incubation. Spots were absent when cells, primary, or secondary anti-cytokine antibodies were omitted from the protocol. Spot number and size can be ascertained using current automated ELISpot reader technology. The frequency of IL-6 and IL-8-producing human fibroblasts could also be determined. For example, 60% of the lung fibroblasts express IL-6, but IL-8 can be detected from only 40% of the cells. Approximately 80% of the human orbital fibroblasts make IL-6, whereas approximately 50% generate IL-8 following IL-1beta stimulation. These new findings show that fibroblasts from different human tissues display different frequencies of cytokine production and this further supports the concept of fibroblast diversity. The sensitivity of this new ELISpot assay is adequate for cytokine detection in just a few cells, unlike the standard ELISA. It should permit ascertaining the frequency of fibroblasts and other adherent cells that produce cytokines and, if desired, can be used in tandem with a standard ELISA to determine total cytokine produced. Moreover, the assay is suitable for normal human adherent cells that are often short-lived and difficult to cultivate. 相似文献
995.
Cell proliferation may be evaluated by various methods, including Ki-67 immunohistochemistry and measures of telomerase activity. Both methods would theoretically show comparable increases in a given case. To evaluate the relationship between these 2 markers of proliferation in aggressive mature B-cell lymphomas, 48 cases were studied. The study group included 5 cases of mantle cell lymphoma (MCL); 6 cases of Burkitt's/Burkitt's-like lymphoma (BL); 9 cases of follicular lymphoma, grade 3 (FLC); and 28 cases of diffuse large B-cell lymphoma (DLC). Telomerase activity was measured as total product generated (TPG) units, and TPG results for the aforementioned cases were compared to the TPG results for 10 cases of reactive follicular hyperplasia. An overlap in TPG scores between reactive cases and lymphoma cases was found. Significant differences in both log TPG (P = 0.0443) and Ki-67 (P = 0.0006) were seen in the different lymphoma types. A positive correlation between Ki-67 percentage and TPG score was identified in FLC (r = 0.9281; P = 0.0003), but a poor correlation between these 2 indicators was seen in the other lymphoma types. Cluster analysis identified distinct patterns for MCL, FLC, and BL, but heterogeneous patterns for DLC. Because increases in both Ki-67 proliferation and telomerase activity are reported in normal germinal centers (GCs), these tests were also evaluated for usefulness as markers of a GC cell phenotype. Among the FLC and DLC cases, features of a GC phenotype significantly correlated with increased Ki-67 percentage (P = 0.0152), but not with increased log TPG. An elevated log TPG correlated with CD10 expression, and elevated Ki-67 percentage correlated with both CD10 and BCL-6 expression. TPG level and Ki-67 percentage did not correlate with the presence of t(14;18) or BCL-2 protein expression. Although the proliferation patterns were fairly distinctive for MCL, FLC, and BL, these studies show that markers of cell proliferation do not by themselves,identify distinct subtypes of large cell lymphomas. With the exception of FLC, the tumors exhibited poor correlation between telomerase activity and Ki-67 proliferation index. These tests did show some correlation with expression of GC cell phenotypic markers, however. 相似文献
996.
A 2-week efficacy and safety study of eszopiclone in elderly patients with primary insomnia 总被引:6,自引:0,他引:6
STUDY OBJECTIVES: Evaluate the efficacy of eszopiclone in primary insomnia. DESIGN/SETTING: Randomized, double-blind, placebo-controlled multicenter in outpatient setting with weekly visits. PARTICIPANTS: Two-hundred thirty one men and women aged 65 to 85 years (mean age 72.3 years) with primary insomnia, as defined by the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition. INTERVENTIONS: Eszopiclone 1 mg (n = 72), eszopiclone 2 mg (n = 79), or placebo (n = 80) nightly for 2 weeks. MEASUREMENTS/RESULTS: Efficacy was assessed using an interactive voice response system. Following the predefined hierarchical testing strategy, the eszopiclone 2-mg group had a significantly shorter sleep latency compared with placebo over the double-blind period (P = .0034). The eszopiclone 2-mg group had significantly longer total sleep time (P = .0003) and eszopiclone 1-mg group had significantly shorter sleep latency (P < or = .012) compared with placebo. The eszopiclone 1-mg group was not significantly different from placebo on total sleep time or any other secondary efficacy endpoint. Secondary analyses indicated that the eszopiclone 2-mg group had significantly less wake after sleep onset; significantly fewer and shorter in duration daytime naps; and significantly higher ratings of sleep quality and depth, daytime alertness, and sense of physical well-being compared with placebo (P < .05). Eszopiclone was well tolerated. The most frequent treatment-related adverse event was unpleasant taste. CONCLUSION: Nightly treatment with eszopiclone 1 mg effectively induced sleep, while the 2-mg dose was effective in inducing and maintaining sleep. Eszopiclone was well tolerated in elderly patients with primary insomnia, and the sleep efficacy was accompanied by significantly less napping and significantly higher ratings of daytime alertness, sense of physical well-being, and several quality-of-life parameters at the higher dose. 相似文献
997.
Detection of turkey rhinotracheitis virus in turkeys using the polymerase chain reaction 总被引:1,自引:0,他引:1
Six-week-old turkey poults were infected with the virulent UK/3B/85 strain of TRTV. Tracheal and oesophageal swabs were made every 2 to 3 days from groups of five poults and the RNA extracted. The TRTV RNA was then reverse-transcribed into complementary DNA (cDNA) using an oligonucleotide complementary to the 3' end of the fusion protein (F) mRNA. The cDNA was then used in a polymerase chain reaction (PCR) with an upstream primer to generate a product of approximately 0.5 kbp which was detected by ethidium bromide staining after electrophoresis. In this way, TRTV was detected in both types of swab for 17 to 19 days post-infection, nearly 2 weeks after the peak titres of infectious virus. Swabs which were allowed to dry completely before RNA extraction were as successful as swabs kept wet and extracted almost immediately, useful for when samples are collected in the field. The oligonucleotides amplified the 0.5 kbp product from TRTV strains isolated in six countries over a 13-year period, indicating that they might be usable as 'universal' oligonucleotides for TRTV detection. 相似文献
998.
Recent studies [8,9] have shown that odors from stressed Norway rats act as signals to which other rats respond primarily by overall changes in activity and exploration. At present the source of these odors is unknown. In this study odors from urine, feces and the bodies of stressed rats were delivered along a runway in which the subjects had been previously trained to run for a water reward in the presence of odors from non-stressed rats. The results indicate that odors are released from the body surface and in the urine but not the feces of stressed rats. 相似文献
999.
1000.
Richard Cooper Ivan Soltero Jeremiah Stamler Louise Mojonnier Yolanda Hall Dorothy Moss David M. Berkson Tom Tokich 《Journal of the National Medical Association》1982,74(4):349-355
Quit-rates for cigarette smokers in a lifestyle intervention program aimed at reducing coronary risk were 24 percent for all participants and 34 percent for non-dropouts. Recidivism remained very low during participation in the program. Half of the smokers who quit did so after being in the program more than two years. These data suggest that while engaging in an effort to make other changes in lifestyle, many smokers can be helped to quit. Sustained antismoking efforts in the clinical practice of medicine can be expected to share these same positive aspects. While mass public health programs to eliminate smoking and prevent young people from taking up the habit are being developed, health practitioners can make a significant contribution by including vigorous efforts at smoking cessation as part of routine practice. 相似文献