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   2957篇
  免费   6篇
电工技术   2篇
化学工业   33篇
金属工艺   3篇
机械仪表   7篇
建筑科学   8篇
能源动力   3篇
轻工业   38篇
水利工程   1篇
石油天然气   2篇
无线电   30篇
一般工业技术   44篇
冶金工业   2774篇
自动化技术   18篇
  2022年   3篇
  2018年   2篇
  2016年   3篇
  2015年   2篇
  2014年   2篇
  2013年   18篇
  2012年   6篇
  2011年   18篇
  2010年   4篇
  2009年   11篇
  2008年   14篇
  2007年   4篇
  2006年   7篇
  2005年   3篇
  2004年   11篇
  2003年   9篇
  2002年   2篇
  2001年   5篇
  2000年   7篇
  1999年   86篇
  1998年   840篇
  1997年   489篇
  1996年   317篇
  1995年   176篇
  1994年   143篇
  1993年   177篇
  1992年   34篇
  1991年   42篇
  1990年   27篇
  1989年   35篇
  1988年   52篇
  1987年   37篇
  1986年   30篇
  1985年   28篇
  1984年   2篇
  1983年   5篇
  1982年   14篇
  1981年   19篇
  1980年   23篇
  1979年   5篇
  1978年   6篇
  1977年   53篇
  1976年   161篇
  1975年   11篇
  1971年   2篇
  1967年   2篇
  1965年   1篇
  1964年   1篇
  1957年   2篇
  1955年   3篇
排序方式: 共有2963条查询结果,搜索用时 406 毫秒
101.
102.
BACKGROUND AND PURPOSE: Transcranial doppler ultrasound (TCD) is used after subarachnoid hemorrhage to detect cerebral vasospasm and is often treated with induced hypertension. Cerebral autoregulation, however, may be disturbed in this population, raising the possibility that TCD velocities may be elevated by induced hypertension. To study this possibility, we performed continuous TCD monitoring of the middle cerebral artery during the induction and withdrawal of induced hypertension in patients after subarachnoid hemorrhage. METHODS: Twenty-eight patients were studied during the induction and withdrawal of hypertension using primarily phenylephrine. Continuous monitoring was performed on the middle cerebral artery with the highest flow velocity. Treatment was based on rising TCD velocities or clinical evidence for cerebral vasospasm. Mean arterial pressure and mean TCD velocities were recorded every minute. A change of > 15% from starting TCD values was considered significant. Cerebral autoregulation was calculated as a percentage of intact autoregulation. Patients were subsequently divided into groups of disturbed and intact autoregulation. RESULTS: In 10 of 19 patients (53%), TCD velocities changed by > 15% and paralleled changes in mean arterial pressure. This directly altered the TCD interpretation of the grade of vasospasm in 7 of 19 patients (36%). Three additional patients had smaller absolute changes in TCD velocities. No clinical difference could be identified between patients with disturbed and intact autoregulation. CONCLUSIONS: In patients with disturbed autoregulation after subarachnoid hemorrhage, induced hypertension can alter cerebral blood flow velocities. The level of autoregulation needs to be considered when interpreting TCD velocities in patients after subarachnoid hemorrhage.  相似文献   
103.
Salmon calcitonin (sCT) is an example of one of the many bioactive peptides that require amidation of the carboxy terminus for full potency. We describe a method for the production of amidated sCT in the mammary gland of transgenic rabbits. Expression of a fusion protein comprising human alpha lactalbumin joined by an enterokinase cleavable linker to sCT was directed to the mammary gland under the control of the ovine beta lactoglobulin promoter. C-terminal amidation in vivo was achieved by extending the sCT by a single glycine residue that provides a substrate for endogenous amidating activity in the mammary gland. Full characterization of the released sCT demonstrated it to be equivalent to synthetic standard in terms of structure, purity, and potency.  相似文献   
104.
Basal cell carcinoma is the most common skin malignancy. While this lesion most often occurs in sun-exposed areas of the skin, it can also develop in sites that are not usually exposed to sunlight or artificial ultraviolet radiation, such as the breast, palm or groin. A periodic complete examination of the skin should be performed to ensure that atypical presentations of basal cell carcinoma are not overlooked or misdiagnosed. Treatment options include curettage and desiccation, cryosurgery, surgical excision, radiotherapy and Mohs micrographic surgery.  相似文献   
105.
During the last 10 years, several cases of myocardial infarction associated with anabolic steroid use have been reported. Postulated mechanisms to explain this association have included changes in lipid levels, the fibrinolytic system, and platelet aggregation. Clenbuterol is a beta 2-agonist with anabolic properties that has not been seen previously with myocardial infarction. We report a case of myocardial infarction in an otherwise healthy 26-year-old body-builder who recently used clenbuterol and anabolic steroids. In this case, synergistic effects of the two agents seem likely to have played a role in the infarct. The normal coronary arteriograms before any anticoagulant or thrombolytic therapy strongly suggest coronary spasm as the mechanism of the infarct.  相似文献   
106.
The previously reported oxytocin antagonist L-371,257 (2) has been modified at its acetylpiperidine terminus to incorporate various pyridine N-oxide groups. This modification has led to the identification of compounds with improved pharmacokinetics and excellent oral bioavailability. The pyridine N-oxide series is exemplified by L-372,662 (30), which possessed good potency in vitro (Ki = 4.1 nM, cloned human oxytocin receptor) and in vivo (intravenous AD50 = 0.71 mg/kg in the rat), excellent oral bioavailability (90% in the rat, 96% in the dog), good aqueous solubility (>8.5 mg/mL at pH 5.2) which should facilitate formulation for iv administration, and excellent selectivity against the human arginine vasopressin receptors. Incorporation of a 5-fluoro substituent on the central benzoyl ring of this class of oxytocin antagonists enhanced in vitro and in vivo potency but was detrimental to the pharmacokinetic profiles of these compounds. Although lipophilic substitution around the pyridine ring of compound 30 gave higher affinity in vitro, such substituents were a metabolic liability and caused shortfalls in vivo. Two approaches to prevent this metabolism, addition of a cyclic constraint and incorporation of trifluoromethyl groups, were examined. The former approach was ineffective because of metabolic hydroxylation on the constrained ring system, whereas the latter showed improvement in plasma pharmacokinetics in some cases.  相似文献   
107.
108.
The characteristics of objective lenses and Ca2+-sensitive probes were examined for imaging with a two-photon laser-scanning microscope (TP-LSM). The brightness of the images of beads taken by different objectives greatly varied and depended predominantly on their numerical aperture (NA) and less on transmittance and chirping effects. Lateral and axial resolutions, dx and dz, defined as the half decay length of fluorescence intensity of the image of a spherical bead (0.3 m) were 0.12 and 0.42 microm (objective; 40x/0.75). They are far better than those of confocal microscopes (0.3 and 1.5 microm, respectively) measured similarly (Kuba et al., 1994). dx linearly increased with an increase in 1/NA, while dz linearly increased with an increase in n/(NA)2 (n, refractive index) except for an objective of large NA (1.3). The coverslip compensation of objective lenses greatly affected the shape of the X-Z scanned images of 5.0 microm beads as well as resolutions, indicating a large effect of spherical aberration. Two-photon excitation spectra of Ca2+-sensitive fluorescent probes, indo-1, fura-2 and Oregon Green BAPTA-1, lied in a wavelength range shorter than twice that activated by one-photon absorption, while emission spectra were unchanged. Three-dimensional images of a cultured hippocampal neurone loaded with Oregon Green BAPTA-1 showed fine structures of spines, dendrites and axons, while imaging with FM1-43 localized presynaptic boutons and demonstrated synaptic vesicle turnover. Dyes bleached little during the recording of 100 sectioned images. These characteristics of TP-LSM as well as its ability to image deeper tissues provide excellent means to study dynamic, spatial changes in intracellular substances and structures. To achieve the good performance of a TP-LSM, however, the relevant usage of appropriate objectives and fluorescent probes are required.  相似文献   
109.
110.
OBJECTIVE: To compare in psychiatric and psychosocial terms the outcome of hysterectomy and endometrial ablation for the treatment of dysfunctional uterine bleeding. DESIGN: Prospective randomised controlled trial. SETTING--Obstetrics and gynaecology department of a large teaching hospital. SUBJECTS: 204 women with dysfunctional bleeding for whom hysterectomy would have been the preferred treatment were recruited over 24 months and randomly allocated to hysterectomy (99 women) or to hysteroscopic surgery (transcervical resection (52 women) or laser ablation (53 women). MAIN OUTCOME MEASURES: Mental state, martial relationship, psychosocial and sexual adjustment in assessments conducted before the operation and one month, six months, and 12 months later. RESULTS: Both treatments significantly reduced the anxiety and depression present before the operation, and there were no differences in mental health between the groups at 12 months. Hysterectomy did not lead to postoperative psychiatric illness. Sexual interest after the operation did not vary with treatment. Overall, 46 out of 185 (25%) women reported a loss sexual interest and 50 out of 185 (27%) reported increased sexual interest. Marital relationships were unaffected by surgery. Personality and duration of dysfunctional uterine bleeding played no significant part in determining outcome. CONCLUSIONS: Hysteroscopic surgery and hysterectomy have a similar effect on psychiatric and psychosocial outcomes. There is no evidence that hysterectomy leads to postoperative psychiatric illness.  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