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   3447篇
  免费   362篇
  国内免费   52篇
耳鼻咽喉   20篇
儿科学   92篇
妇产科学   101篇
基础医学   551篇
口腔科学   76篇
临床医学   470篇
内科学   713篇
皮肤病学   64篇
神经病学   210篇
特种医学   272篇
外科学   425篇
综合类   72篇
预防医学   207篇
眼科学   50篇
药学   314篇
中国医学   9篇
肿瘤学   215篇
  2021年   42篇
  2020年   21篇
  2019年   42篇
  2018年   57篇
  2017年   32篇
  2016年   34篇
  2015年   71篇
  2014年   93篇
  2013年   105篇
  2012年   105篇
  2011年   154篇
  2010年   90篇
  2009年   91篇
  2008年   143篇
  2007年   147篇
  2006年   128篇
  2005年   141篇
  2004年   126篇
  2003年   118篇
  2002年   113篇
  2001年   110篇
  2000年   99篇
  1999年   103篇
  1998年   80篇
  1997年   71篇
  1996年   86篇
  1995年   70篇
  1994年   54篇
  1993年   46篇
  1992年   74篇
  1991年   89篇
  1990年   75篇
  1989年   98篇
  1988年   103篇
  1987年   84篇
  1986年   76篇
  1985年   75篇
  1984年   69篇
  1983年   44篇
  1982年   47篇
  1981年   33篇
  1980年   36篇
  1979年   42篇
  1978年   26篇
  1977年   25篇
  1976年   28篇
  1975年   27篇
  1974年   19篇
  1972年   22篇
  1971年   20篇
排序方式: 共有3861条查询结果,搜索用时 15 毫秒
1.
In brain regions containing noradrenergic (NA) cell bodies or terminals, DSP-4 induces changes in the activity of catecholamine-synthesizing enzymes which suggest that central NA neurons are lesioned by this neurotoxin. In contrast, the lack of change in the same enzymatic activities in an area containing mostly adrenergic (A) neurons (C2 region), favors the hypothesis of a resistance of the A neurons to DSP-4. Furthermore, the enzymatic changes observed in peripheral organs suggest a peripheral activation of the NA cell bodies in response to lesioning of the sympathetic terminals by DSP-4.  相似文献   
2.
The aim of this study was to assess alcoholic inpatients' smoking and coffee intake variation following withdrawal. Only moderate smokers (less than 30 cigarettes/day) showed a significant increase of cigarette consumption after alcohol withdrawal. However, their urinary cotinine level did not vary, suggesting a behavioral, and not biological, compensation through smoking following alcohol withdrawal. Heavy smokers (30 cigarettes/day or more) showed no significant clinical or biological variation of smoking behavior. Coffee consumption increased after alcohol withdrawal in all patients, irrespective of smoking habits.  相似文献   
3.
The behavioral effects of the antidepressants nomifensine, diclofensine, bupropion, and imipramine were examined using a cocaine substitution drug self-administration procedure in baboons and a cocaine drug discrimination procedure in rats. Intravenous self-administration of the antidepressants was examined in baboons under conditions in which baseline responding was maintained by intravenous injections of cocaine HCl (0.32 mg/kg/injection). Drug was available under a fixed-ratio 80-response or 160-response schedule of intravenous injection. Each drug injection was followed by a 3-h time-out allowing a maximum of eight injections per day. The antidepressants or their vehicles were substituted for cocaine for a period of 15 days, followed by a return to the cocaine baseline. Nomifensine, diclofensine, and bupropion all maintained self-administration behavior at levels above those maintained by their respective vehicles. Some doses of nomifensine, diclofensine, and bupropion maintained levels of behavior similar to those maintained under baseline cocaine conditions. High doses of imipramine maintained levels of behavior above those maintained by its vehicle, but the amount of behavior maintained under these conditions was extremely small. In a second experiment rats were trained to discriminate 32 µmol/kg cocaine (IP 10 min presession) from no drug in a two-lever food reinforced drug discrimination procedure in which responding on one lever was reinforced following ten consecutive responses when the session was preceded by cocaine administration, while responding on the other lever was similarly reinforced in the absence of cocaine pretreatment. Cocaine, nomifensine, diclofensine, and bupropion all dose-dependently occasioned cocaine-appropriate responding. Imipramine did not occasion cocaine-appropriate responding over a range of behaviorally active doses.  相似文献   
4.
Linomide (N-phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxo-quinoline-3- carboxamide) is a quinoline 3-carboxamide which previously has been demonstrated to produce immunomodulator and antitumor effects when given in vivo. To test the possible antitumor effects of linomide against prostatic cancers, rats bearing five distinct Dunning R-3327 rat prostatic cancer sublines were treated daily with i.p. injections of linomide. These studies demonstrated that linomide has a reproducible antitumor effect against all of the prostatic cancers tested regardless of their growth rate, degree of morphologic differentiation, metastatic ability, or androgen responsiveness. This antitumor effect is observed only in vivo, not in vitro, and involves a cytotoxic response of the prostatic cancer cells. This cytotoxic response results in the retardation of the growth rate (i.e., increased tumor volume doubling time) of primary prostatic cancers and in metastatic lesions. Linomide's growth retardation is reversible, and thus continuous daily treatment with linomide is required for maximal antitumor response. Pretreatment of rats with linomide before tumor inoculation has no effect in addition to that produced by initiating linomide treatment at the time of tumor inoculation. No enhancement of either natural killer cell number or natural killer cell cytotoxic activity is induced by linomide treatment in the tumor-bearing rats. In addition, depletion of natural killer cell activity via injections of asialo-GM1 antiserum does not prevent the antitumor effects of linomide in vivo. Likewise, the antitumor effects of linomide are also produced in prostatic cancer-bearing athymic nude rats. These results suggest that the requirement for host involvement in the antitumor effects of linomide against rat prostatic cancers may involve both immune and nonimmune host mechanism(s) (e.g., antiangiogenesis).  相似文献   
5.
6.
BACKGROUND: A simple, rapid, inexpensive method for measuring the flow in a patient's vascular access would permit routine monitoring during haemodialysis, and hence provide information of access graft deterioration sufficiently early to increase the success of minimally invasive remedial procedures. This paper reports the validation of such a method in animals. METHODS: A PTFE graft was implanted in sheep between the carotid artery and the jugular vein. While the sheep was under general anaesthesia and on an haemodialysis circuit, ultrasound velocity in its blood was perturbed by the injection of a 5-10 ml bolus of isotonic NaCl. The pump tubing flow was measured by a transit-time blood flow meter. This flow was combined with the areas of perturbation generated by the injection before and after mixing in the access flow to estimate graft flow. The calculated graft flow was compared to flow measured directly by a transit-time probe on the same carotid artery. RESULTS: Over a 10-fold range, 120-1260 ml/min, graft flow measured by ultrasound velocity dilution agreed well with graft flow measured directly with a scatter of 76 ml/min about the regression line. CONCLUSION: Ultrasound velocity dilution provides a method for measuring flow in the graft accurate enough for clinical evaluation of patients on dialysis.   相似文献   
7.
Three cases in which the temporoparietal fascial flap was used to salvage denuded ear cartilage during the acute period after burn injury are reported. Patients' burns ranged from 30% to 75% total body surface area. The full-thickness burn was acutely excised, exposing the auricular cartilage. The temporoparietal facial flap was elevated and wrapped around the cartilage. The flap was then covered with a split-thickness skin graft. All flaps and skin grafts survived. Additional reconstructive procedures have been performed on two of the patients and are planned for the third.  相似文献   
8.
An international collaborative study was carried out to determine the suitability of the current WHO II-IX-X concentrate standard, 84/681, for assigning potency to the more highly purified factor IX concentrates. Three Coagulation Factor IX (Human) preparations and one Factor IX Complex preparation were assayed by the one stage method against WHO 84/681 following predilution to 1.0 u/ml in buffer, 1% albumin, or factor IX deficient plasma. There were no cases of non-parallelism between any of the preparations and the current WHO standard. Predilution of the Coagulation Factor IX (Human) preparations in 1% albumin or factor IX deficient plasma gave similar potency values. Predilution in buffer gave significantly lower (p less than 0.01) potency values. For the Factor IX Complex preparation, potency estimates were significantly different (p less than 0.01) with each prediluent. The overall precision was similar within each predilution for all preparations with predilution in buffer being less precise than predilution in albumin or in deficient plasma. WHO standard 84/681 appears to be a suitable standard for the potency determination of the more highly purified factor IX preparations. Predilution in 1% albumin or factor IX deficient plasma is recommended as they give equivalent results with the least variability.  相似文献   
9.
W A Wallace  J A Schofield  D Lamb    S E Howie 《Thorax》1994,49(11):1139-1145
BACKGROUND--Cryptogenic fibrosing alveolitis (CFA) is believed to have an immunological pathogenesis with a persisting inflammatory reaction to an as yet unidentified pulmonary antigen(s). A high frequency of IgG autoantibodies has previously been found in the plasma of patients with CFA to an extractable 70-90 kDa lung antigen by Western blotting. Preliminary immunohistochemical studies with patient IgG had indicated that the target protein(s) might be associated with alveolar epithelial lining cells which have previously been suggested as the site of immunological attack in CFA. METHODS--In order to confirm this finding immunohistochemical analysis and Western blotting were performed on a human type II alveolar cell line (A549) using CFA patient plasma. In order to study further the distribution of the antigen, antibodies were raised in a rabbit to the partially purified 70-90 kDa CFA lung protein. RESULTS--The results showed that the human CFA autoantibody recognised a 70-90 kDa protein with a cytoplasmic distribution present in the A549 cells, confirming previous observations. The immune rabbit IgG recognised a protein of similar molecular weight by Western blotting of protein derived from lung biopsy samples of patients with CFA and A549 cells. In addition it immunoprecipitated protein(s) of this molecular weight from lung biopsy protein extracts from patients with CFA. The precipitated protein(s) were found to cross-react with the autoantibody found in the plasma of patients with CFA. Immunohistochemical analysis with immunised rabbit antibody revealed positive staining of type I and II alveolar epithelial lining cells in CFA. A similar pattern of epithelial staining was also observed with the rabbit IgG on biopsy specimens of lung from patients with sarcoidosis and control lung tissue, although this was more focal and less intense. No positive staining was seen on sections from a number of non-pulmonary tissues (colon, liver, kidney, tonsil, lymph node, skin, cervix). Cytoplasmic staining of the A549 cell line was also detected. CONCLUSIONS--The 70-90 kDa protein recognised by autoantibodies in patients with CFA is associated with pulmonary epithelial lining cells. The immune rabbit IgG produced appears to recognise antigen by Western blotting and immunohistochemical staining of lung tissue in a similar pattern to the patient autoantibodies. Immunohistochemical data obtained with this antibody suggest that the putative autoantigen against which patients with CFA mount a humoral immune response may be endogenous and specific to the lung.  相似文献   
10.
Between 1968 and 1985, 80 children underwent correction of total anomalous pulmonary venous drainage. There were 47 boys and 33 girls whose ages ranged from 3 days to 16 years (median 2 months, interquartile range 5 years). Seventy (87.5%) were less than 1 year of age at operation. Fifty-eight (72.5%) weighed less than 5 kg, the range being 1.6 to 42 kg (median 3.7 kg, interquartile range 2.4 kg). Forty-five (56%) patients had supracardiac, 14 (17.5%) cardiac, 15 (19%) infracardiac, and 6 (7.5%) had mixed total anomalous pulmonary venous drainage. Follow-up was complete in 78 (97.5%) and ranged from 6 to 189 months (median 58 months, interquartile range 59 months). There were 14 (17.5%) early and six (7.5%) late deaths. Analysis by various factors revealed year of operation as the only factor to affect survival at the 5% level of significance. Early mortality was 29% between 1968-1977 and 11% between 1978-1985 (p = 0.04). Postoperative pulmonary venous obstruction occurred in five (6%) patients between 6 weeks and 3 months after operation. All 5 died, three after reoperation. Five (6%) other children had reoperations, four for residual shunts and one for superior vena caval obstruction.  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