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   3627篇
  免费   2篇
综合类   3篇
化学工业   9篇
机械仪表   1篇
建筑科学   2篇
轻工业   2篇
无线电   3篇
一般工业技术   4篇
冶金工业   3597篇
自动化技术   8篇
  2017年   1篇
  2016年   1篇
  2010年   1篇
  2008年   2篇
  2007年   1篇
  2006年   1篇
  2004年   1篇
  2003年   5篇
  2002年   1篇
  2000年   1篇
  1999年   125篇
  1998年   1119篇
  1997年   622篇
  1996年   426篇
  1995年   216篇
  1994年   182篇
  1993年   195篇
  1992年   33篇
  1991年   61篇
  1990年   59篇
  1989年   51篇
  1988年   54篇
  1987年   56篇
  1986年   26篇
  1985年   39篇
  1983年   2篇
  1982年   18篇
  1981年   19篇
  1980年   26篇
  1979年   5篇
  1978年   8篇
  1977年   76篇
  1976年   191篇
  1975年   3篇
  1955年   2篇
排序方式: 共有3629条查询结果,搜索用时 0 毫秒
101.
Application software for Intel's 8052AH-basic microcontroller can be developed in MCS basic-52, an enhanced version of basic, using the onchip basic interpreter. The paper explores the 8052AH-basic device and its language in comparison with the standard Microsoft basic and presents some software routines and other guidelines for programmers. Control-oriented applications, as opposed to conventional number-crunching applications, are emphasized. The paper also discusses how the resources of the Intellec development system can be used to facilitate the development of application software.  相似文献   
102.
103.
104.
PURPOSE: There is no consensus in the literature regarding the role of lymphangiography in promoting hypothyroidism in individuals with Hodgkin's disease irradiated with a mantle field. We sought to analyze the onset and rate of developing clinical or chemical hypothyroidism as well as possible factors related to its development in patients who received irradiation to the thyroid gland during treatment of Hodgkin's disease. METHODS AND MATERIALS: One hundred and forty-two patients with Hodgkin's disease were treated at the Fox Chase Cancer Center between June 1967 and October 1993. All patients were treated with curative intent with radiation therapy using a mantle field. After exclusion of patients without available thyroid function tests, < 200 days of follow-up, or no radiation to the thyroid, 104 patients were eligible for analysis. Follow-up ranged from 7-170 months (median: 43 months). Sixty-seven patients had a lymphangiogram. Seventy-three patients were treated with radiation alone and 31 with radiation plus chemotherapy. RESULTS: The actuarial 2-, and 5-year rates of biochemical hypothyroidism for all 104 patients were 18 and 37%, respectively. Forty patients developed hypothyroidism: 9 (23%) at < or = 1 year, 18 (45%) at < or = 2 years, and 33 (83%) at < or = 5 years. The actuarial 2-, and 5-year rates of biochemical hypothyroidism for patients who underwent a lymphangiogram were 23 and 42%, respectively, compared to 9 and 28%, respectively, for patients who received mantle irradiation without a lymphangiogram (p = 0.05). The effects of lymphangiogram, total thyroid dose, stage, chemotherapy, dose per fraction, energy, and age were evaluated for all patients by Cox proportional hazards regression analysis. The use of a lymphangiogram (p = 0.05) was the only variable that significantly influenced hypothyroidism. CONCLUSIONS: This paper demonstrates in a multivariate analysis accounting for other potentially important variables the significant effect of lymphangiography and subsequent radiation therapy on the development of hypothyroidism. This information must be balanced with the fact that lymphangiograms remain a useful aid in assessing lymph node involvement, staging patients, and planning treatment fields.  相似文献   
105.
Two randomized, double-blind clinical trials in dogs with spontaneous appendicular osteosarcoma treated with combination chemoimmunotherapy are reported. In both trials, dogs without overt metastasis underwent complete amputation of the affected limb. In trial 1, 40 dogs were treated with cisplatin chemotherapy [(CDDP), 70 mg/m2 i.v. every 28 days x 4]. Following CDDP, dogs without evidence of overt metastasis (n = 25) were randomized to receive liposome-encapsulated muramyl tripeptide phosphatidylethanolamine ](L-MTP-PE), 2 mg/m2 i.v.) or placebo liposomes (lipid equivalent) twice weekly for 8 weeks. Of 14 dogs in the placebo group, 13 (93%) died of metastasis; the median survival time was 9.8 months. Of 11 dogs in the L-MTP-PE group, 8 (73%) developed metastasis; the median survival time was 14.4 months, which was significantly longer than that of the placebo group (P < 0.01). In trial 2, 64 dogs received CDDP (70 mg/m2 i.v. every 21 days x 4) and were randomized to concurrently receive L-MTP-PE (2 mg/m2 i.v.) twice or once weekly, or placebo liposomes once weekly for 8 weeks. Median survival times were 10.3, 10.5, and 7.6 months, respectively. There were no significant differences among the three treatment groups in trial 2. Survival times for dogs receiving L-MTP-PE in trial 1 were significantly longer than those for dogs in trial 2 that received four doses of CDDP concurrently with twice weekly L-MTP-PE (P < 0. 04). The results of the first trial confirm our previous observation that L-MTP-PE has antimetastatic activity in dogs with osteosarcoma when given following amputation. The results of the second trial demonstrate that there is no survival advantage of administering L-MTP-PE concurrently with CDDP.  相似文献   
106.
BACKGROUND: Germ cell tumors, the most common ovarian malignancies in females under the age of 21, are rare in older women. We report an unusual case of a mixed embryonal carcinoma and endodermal sinus germ cell tumor in a perimenopausal patient and review the differential diagnosis and management of these malignancies with respect to age. CASE: A 53-year-old woman complaining of irregular menses and pelvic pain was found to have a large pelvic mass and a positive pregnancy test. Subsequent investigation revealed a large left adnexal mass, and an elevated beta-HCG and alpha-AFP. At laparotomy, a mixed germ cell tumor was found. The patient was treated with multiagent chemotherapy and currently is without evidence of disease. CONCLUSION: Although rare, the diagnosis of germ cell tumor should be considered in older women presenting with a large pelvic mass. The treatment and prognosis is similar regardless of age, except that reproductive-sparing surgery is not a priority in the older patient.  相似文献   
107.
Using an atomic force microscope, supported bilayers of saturated phosphatidylcholine (in the gel state) containing various amounts of gramicidin A (gA) were imaged in aqueous solutions and at room temperature. gA clusters were directly observed for the first time under these conditions. It was found that, at a lower gA concentration, gA aggregated into domains, composed of small clusters along with a considerable amount of lipids. This basic aggregation unit, most likely a hexamer, remained the same for acyl chain lengths from 14 to 18 carbons. These small clusters were observed to form elongated aggregates (line type) but never into extended pure gA domains. When gA concentrations were increased, for bilayers with 16 carbons or less, gA aggregated into larger domains but the basic unit remained separated by lipid molecules. At about 5 mol % gA, a percolation-like transition occurred at which the line type aggregates were connected to each other. However, for bilayers with more than 16 carbons, multiple lamellar structures were formed at higher gA fractions and the top layer had a ripple-like surface morphology. The molecular mechanism for the formation of these peculiar structures remains to be elucidated.  相似文献   
108.
OBJECTIVE: To explore possible effects of aging on the excitability of spinal reflexes. DESIGN: Using a cross-sectional design, the influences of muscle vibration and the Jendrassik maneuver on patellar tendon reflex function were compared between 30 young adults and 15 older adults. SETTING: Motor control research laboratory. SUBJECTS: The young adults were volunteers of college age. The older adults (74.5 +/- 4.14 yr) were volunteers from the local community. All subjects were free of medications and neurological conditions that would affect normal neuromuscular responses. MAIN OUTCOME MEASURES: A force-time curve analysis of the patellar tendon reflex response was used to assess the inhibition and facilitation of spinal reflexes. In the experimental protocol to assess spinal reflex inhibition, 100 Hz vibration was applied to the right quadriceps muscle. In another experimental protocol, spinal reflex facilitation was assessed using the Jendrassik maneuver. To perform the Jendrassik maneuver, subjects were instructed to grasp their hands together and to pull as hard as possible while breathing normally. After a 2-second count, the tendon tap was delivered to the right leg and the subject was instructed to relax. In both experimental protocols, control patellar tendon reflexes were collected. RESULTS: Analysis of variance for reflex peak force revealed a significant 30% reduction in the amount of vibration-induced reflex inhibition with increasing age, and a similar 33% reduction in the amount of Jendrassik maneuver facilitation observed for the older adults as compared with the younger adults. CONCLUSION: These results support the hypothesis that inhibitory and excitatory influences acting on the alpha motoneuron pool are different in young and older adults.  相似文献   
109.
Electroretinographic (ERG) spectra show that juvenile goldfish have ultraviolet (UV) sensitivity but adults do not. Chromatic adaptation data suggest mediation by UV cones. ERG spectra from eye cups and spectrophotometry of lenses show that the loss of UV sensitivity with age does not result from lens changes. Our results contribute to a growing literature on UV cone mechanisms and visual development in fish.  相似文献   
110.
In 12 depressed inpatients referred for bilateral electroconvulsive therapy (ECT), each patient was titrated at the first treatment session by using an ascending method-of-limits procedure with a step-wise increase in pulse frequency (frequency titration) or train duration (duration titration). At the second treatment session, seizure threshold was redetermined by using the method (frequency or duration titration) not used at the first treatment. Frequency or duration was maintained at the lowest level when the other parameter was titrated. Seizure threshold was significantly lower with duration titration (mean, 90 mC; SD, 27.3) than frequency titration (mean, 114 mC; SD, 35.6; p = 0.03). On average, patients in the duration-titration group required 1.2 (SD, 0.6) subconvulsive stimulations before a seizure was elicited, and patients in the frequency-titration group required 1.7 (SD, 0.9) subconvulsive stimulations before a seizure was elicited, a nonsignificant difference. These findings suggest that to elicit a seizure during ECT, increasing train duration may be slightly more efficient than increasing frequency. Basic and other clinical research findings indicate that increasing pulse width may be an inefficient way to elicit a seizure. Therefore the following sequence in the determination of seizure threshold is worth considering when using dose-titration or related techniques: the train duration should be increased first before increasing pulse frequency, and the decision to increase pulse width should be reserved for patients who do not seize at the maximal duration and frequency settings. Further empiric research is needed to establish the utility of this approach.  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