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   3405篇
  免费   20篇
  国内免费   6篇
电工技术   23篇
综合类   3篇
化学工业   230篇
金属工艺   16篇
机械仪表   16篇
建筑科学   53篇
矿业工程   1篇
能源动力   20篇
轻工业   132篇
水利工程   8篇
石油天然气   40篇
武器工业   1篇
无线电   97篇
一般工业技术   243篇
冶金工业   2435篇
原子能技术   12篇
自动化技术   101篇
  2023年   7篇
  2020年   10篇
  2019年   10篇
  2018年   12篇
  2017年   9篇
  2016年   9篇
  2014年   14篇
  2013年   38篇
  2012年   29篇
  2011年   69篇
  2010年   38篇
  2009年   34篇
  2008年   45篇
  2007年   36篇
  2006年   35篇
  2005年   37篇
  2004年   32篇
  2003年   48篇
  2002年   48篇
  2001年   33篇
  2000年   25篇
  1999年   119篇
  1998年   686篇
  1997年   414篇
  1996年   257篇
  1995年   193篇
  1994年   159篇
  1993年   173篇
  1992年   36篇
  1991年   50篇
  1990年   41篇
  1989年   45篇
  1988年   53篇
  1987年   35篇
  1986年   37篇
  1985年   44篇
  1984年   17篇
  1983年   24篇
  1982年   21篇
  1981年   28篇
  1980年   33篇
  1979年   17篇
  1978年   14篇
  1977年   72篇
  1976年   158篇
  1975年   11篇
  1974年   10篇
  1973年   13篇
  1972年   6篇
  1971年   7篇
排序方式: 共有3431条查询结果,搜索用时 15 毫秒
991.
GR Morrow  JT Hickok 《Canadian Metallurgical Quarterly》1993,7(12):83-9; discussion 93-4, 97
Nausea and vomiting associated with chemotherapy most commonly occur after administration of the drug regimen, but a substantial proportion of patients also develop these symptoms in anticipation of treatment, after one or more courses of chemotherapy have been given. Currently available pharmacologic agents are unable to provide complete protection from either anticipatory or post-treatment nausea and emesis associated with cancer chemotherapy. Since anticipatory nausea and vomiting are believed to become conditioned responses through the learning process of classical conditioning, behavioral treatments may be particularly appropriate. Progressive muscle relaxation training is effective in preventing as well as decreasing the frequency of postchemotherapy nausea and vomiting, whereas systematic desensitization has been found to be more effective against anticipatory nausea and emesis. Hypnosis and cognitive distraction have been used mainly in children and adolescents.  相似文献   
992.
This study was conducted to determine the efficacy of the T cell flow cytometry crossmatch (T-FCXM) test in 841 first cadaver donor transplants. Results showed one-year graft survival rates were 82% for T-FCXM-negative patients, compared with 75% for T-FCXM-positive patients (P = 0.01). Early one-month graft failure was 13 percentage points higher in those with a positive T-FCXM than those with a negative T-FCXM. The positive crossmatch patients also had more frequent immunological failures. A positive T-FCXM was found in 39% of the sensitized patients (PRA > 10%) and 8% of those who had not been sensitized. Patients with a positive T-FCXM in either category had a 74% graft survival rate. Thus, most of the T-FCXM-positive results occurred in patients with complement-fixing antibodies. It is suggested that flow cytometry crossmatching (FCXM) be used prospectively, despite the fact that many patients with a positive crossmatch did have successful transplants (TXs). In the current climate of a cadaver kidney scarcity and large recipient waiting pools, utilization of kidneys for patients with the highest probability of success seems a most prudent policy.  相似文献   
993.
RATIONALE AND OBJECTIVES: The authors constructed and evaluated a hybrid cassette for single-exposure extremity imaging with storage-phosphor plates and conventional radiographic film. METHODS: A hybrid cassette was constructed using a fine radiographic screen and a storage-phosphor plate. Exposures of a Lucite step wedge and a line pair gauge were made with the hybrid cassette, a conventional radiographic cassette, and a storage-phosphor cassette. The spatial resolution and imaging speeds of the hybrid and standard systems were compared. RESULTS: Spatial resolution loss was less than 0.5 line pairs per mm with the hybrid cassette. Speed loss was characteristic of the hybrid cassette, requiring approximately 40% greater exposure to produce the same film density as standard cassettes. CONCLUSIONS: The speed difference between this and a previous study is probably due to differences in film-screen choice, kilovolt peak, and storage-phosphor plate generations. The sensitivity spectrum of our film and the emission spectrum of our screens were more closely matched than were the spectra in the previous study; we used lower kilovolt peak, and our storage-phosphor plates were a later, more efficient, generation. Despite slight speed losses, the hybrid cassette appears to be a better choice for obtaining matched images for clinical trials than the alternative of two separate exposures.  相似文献   
994.
BACKGROUND: Reduction of intraocular pressure (IOP) is a primary goal of most glaucoma treatments. However, because the IOP varies during the day, single measurements performed in an ophthalmologist's office do not necessarily provide information on the peak level and fluctuation of the IOP. METHODS: Home tonometry was performed to gain more information on the nature of the diurnal IOP curves and on their variability. One hundred seventy-six patients with open-angle glaucoma (OAG), 55 subjects with ocular hypertension (OHT), and 18 control individuals measured their IOP five times daily at home for 4 to 8 consecutive days using a self-tonometer. RESULTS: Well-defined diurnal IOP variations were observed in all three groups with a predominance of curves with morning or mid-day maxima. Erratic IOP curves without a diurnal rhythm were present in OHT (22%) and OAG (16%) patients but not in control subjects. Differences between the curves of the two eyes of an individual were frequent in OHT (33%) and OAG (36%) patients but not in control subjects (6%). Finally, the majority of OHT (72%) and OAG (66%) patients showed a difference in their diurnal curve patterns on repeat home tonometry performed months apart. CONCLUSION: The authors indicate that it is difficult to rely on one eye as a control for the other. They also indicate that changes in IOP observed in the office at different visits often may be due to a shift in the type of diurnal curve rather than to a true change in the mean IOP. Monitoring of the diurnal IOP may be necessary in some cases if the clinician relies, even partially, on the level of IOP when making a decision on patient management.  相似文献   
995.
We have observed spontaneous development of striae and an enhanced visibility of them after placing rigid gas permeable contact lenses on six patients suspected of having early keratoconus. These fine folds subside upon removal of the rigid lens. This observation assists clinicians with the differential diagnosis of irregular astigmatism when the definitive biomicroscopic signs of keratoconus are either not present or are so subtle that their presence is questionable. Although these striae may not occur in all patients suspected of having early keratoconus, we find that observation of the posterior cornea in the presence of a rigid lens will often confirm the diagnosis of keratoconus. We have not seen similar striae in patients whose clinical presentation is not consistent with early keratoconus.  相似文献   
996.
Increasing demand for blood during elective surgery has led to attempts to rationalize routine preoperative crossmatching to those operations when there is a reasonable (greater than 30%) chance of it being required. Results of a questionnaire returned by 86% of the urology units in Great Britain show that 41% continue to crossmatch 2 units of blood before transurethral prostatectomy. A review of 301 transurethral prostatectomies performed with preoperative grouping and saving of blood showed that only 11% of the patients required transfusion. The need for transfusion was significantly associated with presentation in chronic or acute on chronic retention (p < 0.01), and the operative factors of weight of resection (p < 0.0001) and degree of hemostasis (p < 0.001). Therefore, a policy of routine preoperative blood grouping and saving is safe, and could be widely adopted, leading to financial saving and a decrease in wastage of blood that becomes too old to use.  相似文献   
997.
A multi-disciplinary approach to designing safer healthcare was utilised to investigate risks in the bed-space in elective surgical wards. The Designing Out Medical Error (DOME) project brought together clinicians, designers, psychologists, human factors and business expertise to develop solutions for the highest risk healthcare processes. System mapping and risk assessment techniques identified nearly 200 potential failure modes in hand hygiene, isolation of infection, vital signs monitoring, medication delivery and handover of information. Solutions addressed issues such as the design of equipment, reminders, monitoring, feedback and standardisation. Some of the solutions, such as the CareCentre™, which brings many of the processes and equipment together into one easy to access workstation at the foot of the bed, have been taken forward to clinical trials and manufacture. The project showed the value of the multi-disciplinary and formal human factors approaches to healthcare design for patient safety. In particular, it demonstrates the application of human factors to a complete design cycle and provides a case study for the activities required to reach a safe, marketable product.  相似文献   
998.
A whole blood immunoassay using gold nanoshells   总被引:11,自引:0,他引:11  
A rapid immunoassay capable of detecting analyte within complex biological media without any sample preparation is described. This was accomplished using gold nanoshells, layered dielectric-metal nanoparticles whose optical resonance is a function of the relative size of its constituent layers. Aggregation of antibody/nanoshell conjugates with extinction spectra in the near-infrared was monitored spectroscopically in the presence of analyte. Successful detection of immunoglobulins was achieved in saline, serum, and whole blood. This system constitutes a simple immunoassay capable of detecting sub-nanogram-per-milliliter quantities of various analytes in different media within 10-30 min.  相似文献   
999.
The design, fabrication, and demonstration of a hand-held microchip-based analytical instrument for detection and identification of proteins and other biomolecules are reported. The overall system, referred to as muChemLab, has a modular design that provides for reliability and flexibility and that facilitates rapid assembly, fluid and microchip replacement, troubleshooting, and sample analysis. Components include two independent separation modules that incorporate interchangeable fluid cartridges, a 2-cm-square fused-silica microfluidic chip, and a miniature laser-induced fluorescence detection module. A custom O-ring sealed manifold plate connects chip access ports to a fluids cartridge and a syringe injection port and provides sample introduction and world-to-chip interface. Other novel microfluidic connectors include capillary needle fittings for fluidic connection between septum-sealed fluid reservoirs and the manifold housing the chip, enabling rapid chip priming and fluids replacement. Programmable high-voltage power supplies provide bidirectional currents up to 100 microAlpha at 5000 V, enabling real-time current and voltage monitoring and facilitating troubleshooting and methods development. Laser-induced fluorescence detection allows picomolar (10(-11) M) detection sensitivity of fluorescent dyes and nanomolar sensitivity (10(-9) M) for fluorescamine-labeled proteins. Migration time reproducibility was significantly improved when separations were performed under constant current control (0.5-1%) as compared to constant voltage control (2-8%).  相似文献   
1000.
Loo C  Lowery A  Halas N  West J  Drezek R 《Nano letters》2005,5(4):709-711
Nanoshells are a novel class of optically tunable nanoparticles that consist of a dielectric core surrounded by a thin gold shell. Based on the relative dimensions of the shell thickness and core radius, nanoshells may be designed to scatter and/or absorb light over a broad spectral range including the near-infrared (NIR), a wavelength region that provides maximal penetration of light through tissue. The ability to control both wavelength-dependent scattering and absorption of nanoshells offers the opportunity to design nanoshells which provide, in a single nanoparticle, both diagnostic and therapeutic capabilities. Here, we demonstrate a novel nanoshell-based all-optical platform technology for integrating cancer imaging and therapy applications. Immunotargeted nanoshells are engineered to both scatter light in the NIR enabling optical molecular cancer imaging and to absorb light, allowing selective destruction of targeted carcinoma cells through photothermal therapy. In a proof of principle experiment, dual imaging/therapy immunotargeted nanoshells are used to detect and destroy breast carcinoma cells that overexpress HER2, a clinically relevant cancer biomarker.  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