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   2580927篇
  免费   189246篇
  国内免费   7554篇
耳鼻咽喉   34262篇
儿科学   85164篇
妇产科学   71560篇
基础医学   363436篇
口腔科学   69631篇
临床医学   234182篇
内科学   514729篇
皮肤病学   62442篇
神经病学   213322篇
特种医学   99855篇
外国民族医学   736篇
外科学   386313篇
综合类   50357篇
现状与发展   5篇
一般理论   968篇
预防医学   195837篇
眼科学   56602篇
药学   187905篇
  8篇
中国医学   5331篇
肿瘤学   145082篇
  2021年   19974篇
  2019年   20614篇
  2018年   29273篇
  2017年   22587篇
  2016年   26219篇
  2015年   29499篇
  2014年   40437篇
  2013年   60418篇
  2012年   80217篇
  2011年   84478篇
  2010年   50998篇
  2009年   49141篇
  2008年   79017篇
  2007年   83829篇
  2006年   85561篇
  2005年   81722篇
  2004年   78718篇
  2003年   76039篇
  2002年   73326篇
  2001年   128406篇
  2000年   131329篇
  1999年   110497篇
  1998年   31252篇
  1997年   27919篇
  1996年   28217篇
  1995年   27383篇
  1994年   25067篇
  1993年   23419篇
  1992年   85159篇
  1991年   81563篇
  1990年   78783篇
  1989年   76059篇
  1988年   69468篇
  1987年   67996篇
  1986年   63542篇
  1985年   60510篇
  1984年   44940篇
  1983年   37943篇
  1982年   22456篇
  1981年   19984篇
  1979年   38959篇
  1978年   27439篇
  1977年   23252篇
  1976年   21495篇
  1975年   22813篇
  1974年   26786篇
  1973年   25370篇
  1972年   23749篇
  1971年   21955篇
  1970年   20183篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
We report spectrophotometric methods for quantifying sodium and potassium in serum and plasma without sample pretreatment or solvent-extraction steps. The methods are based on novel chromogenic ionophores characterized by molecular structures highly preorganized for binding, which result in exceptionally high sensitivity and selectivity (negligible responses to sodium at 80 to 200 mmol/L in the potassium assay and to potassium at 0 to 10 mmol/L in the sodium assay). The within-run imprecisions are comparable with those for ion-selective electrodes (for K, 1.0% at 4.5 mmol/L; for Na, 1.1% at 136 mmol/L); the analytical range is 2-10 mmol/L for potassium, 80-170 mmol/L for sodium. The results for greater than 100 patients' samples correlated well with results obtained with ion-selective electrodes (r = 0.99 for K, 0.97 for Na). The ready-to-use aqueous reagents will be available under the trade name of ChromoLyte for use with Technicon's RA family of clinical analyzers.  相似文献   
952.
M Vousden 《Nursing times》1988,84(10):16-17
  相似文献   
953.
Differentiation of cardiac murmurs by dynamic auscultation   总被引:1,自引:0,他引:1  
The techniques described in this monograph will aid in the accurate identification of the origin of a cardiac murmur or abnormal heart sound. They do not necessarily reveal the presence or severity of cardiac disease. No maneuver is 100% accurate in elucidation of cardiac abnormalities, and a given maneuver's effectiveness varies in its application. The systematic application of a combination of maneuvers improves the accuracy of diagnosis. Auscultatory findings must be interpreted with consideration of the total clinical examination including history, other physical findings, ECG, chest x-ray, and possibly an echocardiogram. Thus, the careful physiological approach to the physical examination represents a powerful noninvasive tool that can be used in combination with other information to accurately diagnose cardiac disease in many patients and efficiently direct further evaluation when necessary.  相似文献   
954.
Noise-induced stress as a predictor of burnout in critical care nurses   总被引:2,自引:0,他引:2  
In this study we found that, for 100 critical care nurses, noise-induced occupational stress was positively related to burnout as measured by Jones's Staff Burnout Scale for Health Professionals (r = 0.369, p less than 0.001) and the emotional exhaustion subscale of Maslach's Burnout Inventory (r = 0.300, p less than 0.01). Hierarchical multiple regressions confirmed these results once variance in burnout linked with life stressors and other occupational stressors was accounted for. Furthermore, an interaction term, noise-induced stress X intrinsic sensitivity to noise in the person, did not account for significant variance in burnout once independent variance linked with noise-induced stress was identified. That is, nurses with intrinsic sensitivity to noise were no more at risk for burnout linked with noise-induced stress than were less sensitive nurses. This result is discussed as evidence that there are exceptionally high levels of noise in critical care units. The critical care unit noises that are most distressing to nurses are identified and discussed in terms of stress theory.  相似文献   
955.
A murine monoclonal antibody PASE/4LJ to prostatic acid phosphatase (PAP) was used to immunostain a wide variety of sections of benign and malignant tissues (654 blocks). Non-neoplastic adult and fetal prostatic glands, primary and metastatic prostatic carcinomas, and scattered cells in prostatic and penile urethra were positive. Rat, dog and rabbit prostates were negative. Nine of 400 tumours of non-prostatic origin showed some positivity: 6/36 carcinoids, 1/9 islet cell tumours, 1/55 ovarian adenocarcinomas (serous) and one carcinosarcoma of the lung (epithelial portion). Positive staining was seen in islet cells in 4/5 specimens of normal pancreas, and in 4/9 blocks of normal pancreas surrounding a pancreatic tumour. Loops of Henle, maculae densae, and distal tubules in 10/10 fetal and 2/9 adult kidneys were also positive, with proximal tubules and collecting ducts negative. All other 159 blocks of non-neoplastic adult and fetal tissues were negative. The antibody was also affinity purified from ascitic fluid, and shown not to inhibit the enzyme activity of prostatic acid phosphatase.  相似文献   
956.
131 patients with resectable, node-positive breast cancer were treated at the National Institute for Cancer Research of Genoa, Italy with a systemic adjuvant regimen based on 14 cycles of chemotherapy, immunostimulation with levamisole, and--for postmenopausal patients--hormone therapy with tamoxifen. The present evaluation is performed eleven years after the admission of the first patient: so far, 75 patients (57.3%) have relapsed and 52 (39.7%) have died. An analysis of prognostic factors for relapse and death shows that the number of positive axillary lymph nodes and the dimension of the primary tumor are significantly associated with survival and relapse-free survival, while age and menopausal status are not.  相似文献   
957.
We report for the first time the frequency distributions of HLA-DRB1 and -DQB1 genes in 55 patients with testicular germ cell carcinoma (TGC) using the modified PCR-RFLP method and compare the results with those for 1216 healthy Japanese control subjects. The modified PCR-RFLP method produced accurate, reproducible cleavage patterns that are easily discriminated. HLA-DRB1*0410 was the susceptibility allele (RR = 3.26, P = 0.006) and DQB1*0602 appears to be a candidate protective allele (RR = 0.26, P = 0.02) for TGC in the Japanese. None of the HLA-DRB1 and -DQB1 alleles showed a specific tendency for histological type or clinical stage of the tumours. Previous studies based on serotyping methods failed to show these allelic associations. High-resolution genotyping is essential because the peptide-binding domain of MHC class II molecules is determined more precisely by their genotypes than by their serotypes. In addition, inherent technical difficulties and typing errors of up to 25% make serotyping inefficient. Our results suggest that high-resolution genotyping is a useful genetic marker to determine risk for TGC.  相似文献   
958.
Zusammenfassung  Ein PCR-Nachweis für gentechnisch ver?nderten Mais ?Event 176? der Fa. Ciba-Geigy wurde etabliert. Der Mais enth?lt Gene, die Selbstschutz gegen den Maiszünsler (Delta-Endotoxin-Gen ausBacillus thuringiensis) und Toleranz gegen das Herbizid Basta (Phosphinothricin-Resistenz-Gen ausStreptomyces hygroscopicus) vermitteln. Zudem enth?lt der Mais ein Ampicillin-Resistenz-Gen. Für die Amplifikation von Bereichen aus allen drei Genen wurden PCR-Primer entworfen. Mit Hilfe dieser Primer und mit ?Event 176?-Mais-DNA als Template konnten die entsprechenden Genbereiche in der PCR amplifiziert werden. Die PCR-Produkte wurden sequenziert, um ihre Identit?t zu best?tigen. Mit Hilfe der Delta-Endotoxin-PCR wurden, auch in Gegenwart von 104fachem überschu? nicht gentechnisch ver?nderter Mais-DNA, fünf haploide Genome der ?Event 176?-DNA nachgewiesen.
Identification of genetically modified maize by PCR
Summary  A PCR-test for the genetically modified maize ?Event 176? of Ciba-Geigy was established. The maize contains genes conferring resistance to the European corn borer (delta-endotoxin gene fromBacillus thuringiensis) and tolerance to the herbicide Basta (phosphinothricin resistance gene fromStreptomyces hygroscopicus). The maize contains also an ampicillin resistance gene. Primers were designed and using ?Event 176?-maize-DNA as template internal regions of the three genes were amplified with PCR. The PCR products were sequenced to confirm their identity. Using the deltaendotoxin primers in PCR down to 5 haploid genomes of ?Event 176?-DNA could be detected, even in the presence of a 104fold excess of DNA from non-modified maize.
  相似文献   
959.
The Dundee Memory Clinic was established in 1991. This paper reviews the diagnosis of the first 150 attenders and compares the findings with those of other memory clinics.  相似文献   
960.
Lead poisoning--one approach to a problem that won't go away.   总被引:7,自引:1,他引:6       下载免费PDF全文
A reduction in sources of environmental lead exposure has resulted in substantial declines in mean blood lead concentrations of all age groups in the United States. However, some segments of the population continue to have unacceptable levels of lead exposure and elevated blood lead concentrations. In addition, virtually all residents of industrialized countries have bone lead stores that are several orders of magnitude greater than those of our preindustrial ancestors. Recent studies suggest that these skeletal lead stores adversely affect health and can contribute to reduced birth weights, aggressive behavior in children, and anemia, hypertension, and kidney disease in adults. Evidence is described that demonstrates that an increase in dietary calcium consumption can reduce lead absorption and toxicity from exogenous and endogenous lead exposure. A relatively inexpensive and effective way to reduce the substantial morbidity that will result from widespread lead exposure is by fortification of a variety of foods with low levels of calcium. This approach can complement other efforts to prevent lead exposure and reduce lead toxicity.  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