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   6372篇
  免费   696篇
  国内免费   22篇
耳鼻咽喉   99篇
儿科学   206篇
妇产科学   199篇
基础医学   836篇
口腔科学   109篇
临床医学   937篇
内科学   1186篇
皮肤病学   50篇
神经病学   591篇
特种医学   281篇
外科学   823篇
综合类   125篇
一般理论   5篇
预防医学   672篇
眼科学   92篇
药学   539篇
中国医学   6篇
肿瘤学   334篇
  2021年   98篇
  2020年   65篇
  2019年   93篇
  2018年   90篇
  2017年   84篇
  2016年   84篇
  2015年   114篇
  2014年   152篇
  2013年   187篇
  2012年   282篇
  2011年   319篇
  2010年   174篇
  2009年   133篇
  2008年   278篇
  2007年   271篇
  2006年   290篇
  2005年   298篇
  2004年   272篇
  2003年   247篇
  2002年   261篇
  2001年   262篇
  2000年   262篇
  1999年   200篇
  1998年   82篇
  1997年   72篇
  1996年   69篇
  1995年   58篇
  1994年   53篇
  1993年   62篇
  1992年   177篇
  1991年   143篇
  1990年   163篇
  1989年   140篇
  1988年   126篇
  1987年   119篇
  1986年   106篇
  1985年   111篇
  1984年   75篇
  1983年   69篇
  1982年   35篇
  1981年   53篇
  1979年   71篇
  1978年   64篇
  1977年   47篇
  1976年   36篇
  1975年   40篇
  1974年   52篇
  1973年   81篇
  1972年   67篇
  1970年   42篇
排序方式: 共有7090条查询结果,搜索用时 15 毫秒
51.
Data from 2,903 adult same-sex twin pairs were analysed to investigate whether the genetic determinants of symptoms of panic are different from those underlying the neuroticism personality trait. Our results suggest that much of the genetic variation influencing the physical symptoms associated with panic is of the nonadditive type, perhaps due to dominance or epistasis. In both sexes these nonadditive genetic effects on physical symptoms influence the reporting of "feelings of panic". In males they also account for as much as half the genetic variance in neuroticism. The remainder is additive and also accounts for the balance of genetic variation in "feelings of panic". In females genetic variance in neuroticism is entirely additive but is not an important source of covariation with either panic symptom. Thus, symptoms of panic seem to be shaped in part by unique genetic influences which do not affect other anxiety symptoms. That a substantial part of the genetic variance in neuroticism in males may be due to the nonadditive effects on physical symptoms of panic may help to explain the rather low correlation between the genetic influences found to affect neuroticism in males and their counterparts in females.  相似文献   
52.
Summary The effects of personality characteristics on social support and hence risk of depression are explored in a group of 150 largely working-class mothers, a subsample of 400 women who took part in a prospective study. This established that once those with depression at first interview were excluded, practically all of the onsets of depression in the follow-up year occurred among 150 women with a severe event or major difficulty — that is a provoking agent. It was also found that low self-esteem and lack of support from a core tie at the time of the crisis was associated with a considerably increased risk. In the subsample as a whole, measures of dependency and attitudinal constraints to support taken at first interview were not associated with risk of depression. But, it is argued, any enduring personality traits that play a role in the link between lack of support and depression would most likely be seen in a smaller group, namely those who had had early inadequate parenting. And the most promising lead concerning the role of personality characteristics did in fact emerge in relation to a small high risk group with such parenting. Most of them had low self-esteem, and they appeared to confide in inappropriate and unreliable sources of support at time of crisis.  相似文献   
53.
An improved procedure for chemically decontaminating residues of nitrosoureas and related N-nitroso compounds ("nitrosamides") commonly used in the cancer research laboratory is proposed. Treatment of accumulated wastes with aluminum:nickel alloy powder while progressively increasing the basicity of the medium consistently led to at least 99.98% destruction of each nitrosamide tested. Hazardous diazoalkanes were never detected in yields of greater than 0.1%. The mutagenicity of the completed reaction mixtures was never more than 3 times background except when the N-nitroso compound contained a 2-chloroethyl group. In most cases, the completeness of reaction could be determined chromatographically, not only to demonstrate the disappearance of the starting N-nitroso compound, but also to follow production of identifiable products in sufficient abundance to account for the starting material destroyed; none of the organic products observed was mutagenic in any of the four tester strains used. The procedure described herein proved reliable in two checker laboratories besides our own when applied to mixtures of seven N-nitroso compounds: N-methyl-N-nitroso-p-toluene-sulfonamide; N-methyl-N-nitrosourethane; N-methyl-N-nitrosourea; N-methyl-N'-nitro-N-nitrosoguanidine; N-ethyl-N-nitrosourea; N-ethyl-N'-nitro-N-nitrosoguanidine; and N-ethyl-N-nitrosourethane. All of the other procedures investigated for destruction of nitrosamides, including the widely used approach of dissolving the nitrosamides in alkali, were associated with important disadvantages.  相似文献   
54.
A distinction among reading disabled children based on whether phonetic or semantic deficits predominate has important implications for remediation. Two kinds of reading disability are related to two distinct aspects of the indirect phonological approach used in the vast majority of reading instructions. This approach to determining the meaning is a conversion of the written form of a word to its phonetic counterpart, making the comprehension auditory. Phonetic reading disabled children have a difficulty with the first step in the process, converting the written word to its sound. Semantic reading disabled children can convert the word to its sound, but this does not lead to determining meaning. Significant gains in performance, may occur by using a direct access to meaning, rather than through the intermediary of sound. The Direct Access approach to reading has one premise: Do not use a "word to sound to meaning" approach. The results of a demonstration project indicate the Direct Access approach to reading can be very useful for many reading disabled children.  相似文献   
55.
Accuracy of Spring and Strain Gauge Hand-held Dynamometers   总被引:1,自引:0,他引:1  
The accuracy of two spring gauge and two strain gauge hand-held dynamometers was determined using certified weights. Each dynamometer, which had extensive prior use, was vertically loaded with the certified weights in 5 lb increments from 5-55 lbs. Analysis of variance was used to compare the actual certified weights with the weights measured by each dynamometer. Additionally, Pearson product moment correlations were calculated between the weights measured by each device. The two spring gauge dynamometers measured comparably as did the two strain gauge dynamometers. Only the two strain gauge dynamometers, however, registered (measured) weights not differing significantly from the actual weights with which they were loaded. The correlations between each device's measurements were 0.98 or above. If the dynamometers tested are indicative, strain gauge dynamometers may be more accurate than spring gauge dynamometers after extensive use. J Orthop Sports Phys Ther 1989;10(8):323-325.  相似文献   
56.
The presence of metastases in the regional lymph nodes is the major prognostic factor in breast cancer in the absence of overt distant metastases and is also an important indicator of the need for adjuvant therapy in "early" breast cancer. Currently, the accurate assessment of axillary lymph node status requires axillary dissection which has an associated morbidity. An alternative method of identifying patients who are "node positive" has been developed by means of immunolymphoscintigraphy with s.c. administered radioiodinated monoclonal antibody. The 131I-labeled anti-breast cancer antibody (RCC-1; 400 micrograms) and cold iodine-labeled "blocking" antibody (Ly-2.1; 2 mg which is nonreactive with breast cancer) were injected s.c. into both arms and scintigraphy images were obtained 16-18 h after the injection, using the axilla contralateral to the side of the breast cancer as the control. Studies were reported as positive (and therefore indicative of lymph node metastases) if the amount of background-subtracted radioactive count in the axilla of interest exceeded the normal side by a radio equal to or greater than 1.5:1.0 as assessed by computer analysis. In 38 of 40 patients the findings on scintigraphy were correlated with operative and histopathological findings on the axillary dissection specimen or cytological findings of fine needle aspiration of axillary lymph nodes. In a prospective study of 26 patients, the method is more sensitive (86%) and specific (92%) than preoperative clinical assessment (57% sensitivity, 58% specificity) in the detection of axillary lymph node metastases; and by combining both modalities of assessment, there was an improvement in the sensitivity (100%) but a deterioration in the specificity (50%). There was no significant complication from this essentially outpatient procedure and only 1 of 40 patients developed a human anti-mouse antibody response. This novel and safe method of imaging may become a most useful adjunct in the surgical management of breast cancer.  相似文献   
57.
58.
59.
Flow cytometry immunolabeling, tube agglutination tests, and thin-layer chromatography immunostaining with two different anti-A monoclonal antibodies (anti-A mAb1 and anti-A mAb2) and one anti-B mAb were used to demonstrate differences in expression of the A and B antigens among erythrocytes from type A and four different type AB cats. Although the flow cytometric patterns of reactivity and agglutination scores for erythrocytes from types A and B cats detected with the anti-A and anti-B mAbs were consistent, reactivity among erythrocytes of different type AB cats was variable. By flow cytometric analysis, 99.9% of type A erythrocytes, no type B erythrocytes, 2.5–4.0% of erythrocytes from type AB cats 1, 3, and 4, and 60.7% of erythrocytes from type AB cat 2 had detectable A antigen when anti-A mAb1 was used. In contrast, 86.4% of type A erythrocytes, no type B erythrocytes, 20.2–38.0% of erythrocytes from type AB cats 1, 3, and 4, and 68.5% of erythrocytes from type AB cat 2 had detectable A antigen when anti-A mAb2 was used. In addition, 86.9% of type B erythrocytes, no type A erythrocytes, 83.1–96.8% of erythrocytes from type AB cats 1, 3, and 4, and 73.0% of erythrocytes from type AB cat 2 had detectable B antigen when the anti-B mAb was used. Agglutination scores of type AB cats were comparable to the percent binding on flow cytometry. Thin-layer chromatography immunostains confirmed differences in the amount of A antigen between erythrocyte glycolipids of type A and AB cats and those of type AB cats 1 and 2. These results suggest that at least two different phenotypes exist within the feline AB blood type, which differ in the amount of A antigen expressed on the erythrocyte surface.  相似文献   
60.
BACKGROUND: Although soluble mediators released by basophils in tissue sites contribute to the chronic injury that occurs in hypersensitivity diseases, only limited information is available about how circulating basophils are recruited to tissues. In particular, the interaction of basophils with endothelium under conditions that mimic physiologic flow has not been explored. OBJECTIVE: We sought to identify adhesion molecules regulating the attachment of human basophils to IL-4-activated human umbilical vein endothelial cells (HUVECs) under flow conditions. METHODS: A parallel-plate flow chamber and blocking mAbs were used to define the adhesion molecules involved in the interactions of peripheral blood basophils (PBBs) and cord blood-derived basophils (CBDBs) with IL-4-activated HUVECs and with Chinese hamster ovary (CHO) cell transfectants expressing specific adhesion molecules. A fluorescent ligand specific for very late antigen 4 (VLA-4) was used to directly examine the VLA-4 affinity state of basophils. RESULTS: Flowing PBBs and CBDBs attached to activated HUVECs and to CHO cells expressing P- or E-selectin. However, only CBDBs attached to vascular cell adhesion molecule 1 (VCAM-1)-transfected CHO cells under flow conditions. The attachment of CBDBs to CHO cells was blocked by mAbs directed against E-selectin, P-selectin, and VCAM-1, whereas attachment of PBBs was blocked by E-selectin and P-selectin mAbs. Activating VLA-4 with Mn(2+) on PBBs resulted in adhesion to the VCAM-1-transfected CHO cells, indicating that VLA-4 activity on PBBs can be regulated, at least in part, through affinity changes. The Mn(2+)-induced upregulation of basophil VLA-4 affinity was demonstrated directly by using a fluorescent ligand for VLA-4 and flow cytometry. CONCLUSIONS: The interaction of human CBDBs and PBBs with endothelium under flow conditions is mediated in part by both P- and E-selectin. VLA-4 additionally contributes to the adhesion of flowing CBDBs. However, the affinity of VLA-4 is too low to support the adhesion under flow conditions of unstimulated PBBs.  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