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   8496篇
  免费   51篇
  国内免费   1篇
电工技术   14篇
化学工业   297篇
金属工艺   32篇
机械仪表   34篇
建筑科学   61篇
矿业工程   1篇
能源动力   35篇
轻工业   142篇
水利工程   8篇
石油天然气   4篇
无线电   188篇
一般工业技术   320篇
冶金工业   7230篇
原子能技术   21篇
自动化技术   161篇
  2022年   12篇
  2021年   15篇
  2019年   11篇
  2018年   19篇
  2017年   21篇
  2016年   33篇
  2015年   10篇
  2014年   29篇
  2013年   52篇
  2012年   41篇
  2011年   50篇
  2010年   39篇
  2009年   44篇
  2008年   55篇
  2007年   50篇
  2006年   58篇
  2005年   54篇
  2004年   39篇
  2003年   58篇
  2002年   33篇
  2001年   37篇
  2000年   34篇
  1999年   260篇
  1998年   2445篇
  1997年   1373篇
  1996年   877篇
  1995年   476篇
  1994年   385篇
  1993年   449篇
  1992年   70篇
  1991年   75篇
  1990年   82篇
  1989年   75篇
  1988年   76篇
  1987年   75篇
  1986年   76篇
  1985年   60篇
  1984年   20篇
  1983年   33篇
  1982年   41篇
  1981年   44篇
  1980年   79篇
  1979年   22篇
  1978年   30篇
  1977年   163篇
  1976年   315篇
  1975年   27篇
  1974年   13篇
  1973年   14篇
  1965年   9篇
排序方式: 共有8548条查询结果,搜索用时 15 毫秒
991.
992.
Immunohistochemistry using monoclonal antibodies against human inhibin, a peptide hormone produced by ovarian granulosa cells to inhibit follicle-stimulating hormone (FSH), has been recently applied to diagnostic anatomic pathology. This investigation hypothesizes that inhibin immunohistochemistry will aid in the crucial clinical distinction between sex cord-stromal and other primary ovarian neoplasms. Available H&E slides and clinical information from a retrospective surgical series of 186 primary ovarian tumors were reviewed to verify diagnoses, and representative paraffin sections were immunostained with anti-inhibin (R1 monoclonal, Serotec, Kidlington, Oxford, UK). Immunoreactivity was graded as weak/strong (W/S), and the proportion of strong staining cells was coded as follows: S1 = <10%, S2 = 10%-50%, S3 = >50%, respectively. Inhibin immunoreactivity for 137 sex cord-stromal lesions was as follows: 100% of 66 granulosa cell tumors: 80% S3, 20% S2; 100% of 17 Sertoli-stromal tumors: 90% S3, 10% S2; 100% of 13 hyperplastic follicular/stromal lesions: 90% S3, 10% S2; 100% of six steroid cell tumors: 100% S3; 90% of 18 thecomas: 40% S3, 10% S2, 10% S1, 30% W; 0% of 12 fibromas, three myxomas, and two sclerosing stromal tumors. None (0 of 49) of the other ovarian neoplasms exhibited inhibin: 22 carcinomas, 12 carcinosarcomas, seven small cell carcinomas, six germ cell tumors, and two lymphomas. In the typical case, the distinction between sex cord-stromal and other ovarian neoplasms requires nothing more than routine pathological examination. In diagnostically challenging cases, our data indicate that inhibin immunohistochemistry is a very useful adjunct because granulosa and sertoli-stromal tumors are positive whereas other potential mimickers have been negative thus far.  相似文献   
993.
BACKGROUND AND OBJECTIVE: Allogeneic bone marrow transplantation (BMT) is the most common treatment for young patients with severe aplastic anemia (SAA). Late graft failure represents one of the possible unfavorable outcomes in this setting. Mixed chimerism might represent a risk factor for late graft failure. We examined this relationship by studying chimerism in long-term survivor SAA patients after allogeneic BMT. METHODS: We analyzed long-term hematopoietic chimerism in 15 patients who received BMTs for SAA: 9 with an irradiation-based conditioning regimen and 6 with ATG. We used a PCR method targeting VNTR loci. Sensitivity of the technique ranged between 0.5 and 1.5%. RESULTS: All patients conditioned with radiation-based schemes showed complete donor chimerism. Conversely, out of six patients who received cyclophosphamide and ATG as a conditioning regimen, only one of them had late graft failure (day +168). In this patient, durable mixed chimera status was first detected two months after BMT. INTERPRETATION AND CONCLUSIONS: Our results suggest that in long-term survivors of SAA after BMT there is almost always complete donor chimerism in both irradiated and ATG-conditioned recipients. Mixed chimerism might predict graft failure in these patients.  相似文献   
994.
We assessed the effects of vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP), and bradykinin in arteries (diameter approximately 230 microns) isolated from cancellous bone from pigs. Arterial segments (2 mm long) were mounted on a myograph for measurement of isometric force development. After submaximal precontraction with norepinephrine, VIP (10(-10)-10(-7) M), CGRP (10(-11)-10(-7) M), SP (10(-6) M), and bradykinin (10(-11)-10(-6) M) were added. 44 arterial segments (23 pigs) were investigated. VIP-, CGRP-, and bradykinin induced a concentration-dependent vasorelaxation, while SP mediated a transient relaxation. After mechanical removal of the endothelium, the effects of SP and bradykinin were completely abolished, while the relaxation to CGRP was still pronounced. This indicates that the effects of SP and bradykinin are mediated by the endothelium, while CGRP mainly mediates relaxation by a direct effect on vascular smooth muscle cells. The relaxations to CGRP and bradykinin were still significant after inhibition of nitric oxide synthase with 10(-4) M N omega-nitro-L-arginine (L-NNA) and inhibition of prostaglandin synthesis with 10(-5) M indomethacin, indicating the existence of an alternative vasorelaxing pathway. Our findings support the theory of a vasoregulatory role of neuropeptides in bone.  相似文献   
995.
The study investigated the psychological health level and related psychosocial factors of nurses. Through cluster sampling, 650 clinical nurses, who come from 5 city hospitals in Changsha, were interviewed with the Symptom Check List-90 (SCL-90), The Life Event Scale, Type A Behavior Questionnaire, and The Social Support Rating Scale. The results indicated that subjects' average symptom score and most factor scores of SCL-90 were significantly higher than that of the chinese norm. Somatization, depression, and obsession are common psychological problems of the clinical nurses, and the psychological health level of middle age group was significantly lower than that of other groups. Regression analysis (both single factor and multiple factors) suggested that TH and CH scores on Type A Questionnaire as well as life event score on the life event score were negatively related to psychological health level while social support score was positively related to it. The influences of psychosocial factors on psychological health level of clinical nurses were discussed.  相似文献   
996.
997.
998.
999.
OBJECTIVES: To investigate whether the isolated urinary bladder spontaneously releases substance P (SP) or bradykinin (BK), which can act as potent mediators of pain and inflammation of the urinary bladder, and whether peptidase inhibitors enhance peptide release. MATERIALS AND METHODS: Urinary bladder segments (2 x 10 x 0.8-1 mm) were isolated from guinea pigs and studied in vitro; tissue contraction was assessed using force-displacement transducers and the release of peptides by specific enzyme immunoassays. RESULTS: In the absence of any exogenous agonists, the inhibition of neutral endopeptidase and angiotensin-converting enzyme by phosphoramidon and captopril, respectively, increased the frequency and magnitude of spontaneous motility of isolated bladder strips. Phosphoramidon increased the net release of SP-like immunoreactivity (SP-LI) and captopril increased the net release of SP-LI and BK-LI, concomitant with contraction. Peptide-LI was recovered primarily from bladder mucosa and to a lesser degree from detrusor smooth muscle. Similarly, peptidase inhibitors primarily affected the bladder mucosa; phosphoramidon induced a fourfold increase in SP-LI and captopril induced a significant increase of SP-LI and BK-LI from the mucosa. Tissues contracted in response to peptidase inhibitors in the presence of atropine and indomethacin, but contraction was reduced significantly by in vitro capsaicin desensitization or removal of bladder mucosa. BK stimulated SP-LI release from mucosa but not detrusor. SP stimulated increased BK-LI release from mucosa and detrusor. CONCLUSIONS: These findings indicate the basal release of peptide-like immunoreactivity by isolated bladder and further support the concept that peptidases located in the bladder mucosa are important in terminating the effects of endogenous peptides.  相似文献   
1000.
Revascularization for arterial stenosis in varied anatomic sites exposed to therapeutic radiation has been well described. In most circumstances, symptomatic end organ ischemia has been the indication for surgical intervention. We report the case of a patient who had symptomatic carotid stenosis 40 years after having ipsilateral neck dissection with radiation therapy. We did a saphenous vein graft interposition and free flap reconstruction of the overlying damaged skin.  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