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   27468篇
  免费   991篇
  国内免费   321篇
电工技术   470篇
综合类   545篇
化学工业   4089篇
金属工艺   537篇
机械仪表   758篇
建筑科学   892篇
矿业工程   181篇
能源动力   609篇
轻工业   2339篇
水利工程   257篇
石油天然气   183篇
武器工业   27篇
无线电   2526篇
一般工业技术   3013篇
冶金工业   9128篇
原子能技术   181篇
自动化技术   3045篇
  2023年   133篇
  2022年   421篇
  2021年   541篇
  2020年   309篇
  2019年   381篇
  2018年   431篇
  2017年   401篇
  2016年   448篇
  2015年   393篇
  2014年   592篇
  2013年   1115篇
  2012年   884篇
  2011年   1085篇
  2010年   814篇
  2009年   866篇
  2008年   870篇
  2007年   876篇
  2006年   744篇
  2005年   643篇
  2004年   714篇
  2003年   931篇
  2002年   1208篇
  2001年   1029篇
  2000年   609篇
  1999年   715篇
  1998年   3031篇
  1997年   1794篇
  1996年   1232篇
  1995年   775篇
  1994年   618篇
  1993年   669篇
  1992年   239篇
  1991年   215篇
  1990年   221篇
  1989年   198篇
  1988年   204篇
  1987年   182篇
  1986年   171篇
  1985年   216篇
  1984年   88篇
  1983年   101篇
  1982年   111篇
  1981年   130篇
  1980年   152篇
  1979年   69篇
  1978年   66篇
  1977年   260篇
  1976年   529篇
  1975年   56篇
  1973年   53篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We report a 20-year-old man affected by glycogenosis type III with distal muscle weakness, more severe in distal leg muscles. The electromyogram showed myopathic features. Nerve conduction studies and central motor conduction after magnetic stimulation of the brain were normal. Our results suggest that there is no involvement of central motor pathways in this disease.  相似文献   
92.
In a previous study we have demonstrated that endogenous neurotrophin 3 (NT3) is required for the survival of most sympathetic neurones in postnatal rats. However, the mechanisms underlying the action of NT3 on sympathetic neurones is not known. Neither is it understood whether NT3 is retrogradely transported from peripheral tissues or acts locally in an autocrine fashion. In the present study, NT3-mRNA was quantified in sympathetic effector tissues and NT3 protein was localized in intact and lesioned sympathetic nerves in rats. NT3-mRNA is expressed and developmentally regulated in many effector tissues including mesenteric arteries, salivary gland, heart and kidney but hardly detectable in the superior cervical ganglia of adult animals. The majority of sympathetic neurones express immunoreactivity for TrkA and TrkC in both neonatal and adult rats. Sympathetic somata are normally immunoreactive for NT3, but the immunoreactivity is abolished by systemic administration of NT3 antibodies or axotomy of postganglionic neurones, suggesting an accumulation of NT3 from extraneuronal sources. Furthermore, the detection of NT3-immunoreactivity in the internal carotid nerve as early as 3 h following a compression and only on the distal side indicates endogenous NT3 is retrogradely transported by sympathetic neurones. These studies provide evidence indicating that NT3, like nerve growth factor, is an effector tissue-derived neurotrophic factor for sympathetic neurones both during development and in the adult animal. Thus, we have provided a clear example that one type of neurone derives, through a retrograde transport mechanism, two neurotrophic factors simultaneously from its peripheral effector tissues.  相似文献   
93.
PURPOSE: Expression of the multidrug resistance gene (MDR1) p170 protein is frequent in leukemic blasts from patients with relapsed acute myelogenous leukemia (AML). A phase I study using the nonimmunosuppressive MDR1 blocker SDZ PSC-833 (PSC) in combination with mitoxantrone (MITO) and etoposide (VP) was performed. PATIENTS AND METHODS: Starting doses (LVL0) of MITO (3.25 mg/m2/d on days 1 and 3 to 6) and VP (210 mg/m2/d on days 1 and 3 to 5) were 40% of the maximal-tolerated dose (MTD) from a prior study. A 1.5-mg/kg loading dose of PSC was followed by a 120-hour continuous infusion of 10 mg/kg/d on days 2 to 6. Blood samples for PSC, MITO, and VP pharmacokinetics (PK) were taken on days 1 and 3, and samples for MDR1 expression were taken on day 0. RESULTS: Severe mucositis developed in all patients at LVL0; therefore, MITO and VP doses were reduced to 2.5 and 170 mg/m2 (LVL-1) for the next seven patients, and this dose proved to be MTD. All LVL0 and three LVL-1 patients had transient elevations in the serum bilirubin level to > or = 4 mg/dL. Serum creatinine level increased to greater than 2 mg/dL in one case. There were no other grade 3 or 4 nonhematologic toxicities observed. The peripheral blood was cleared of leukemia in three LVL0 and four LVL-1 patients. The marrow was cleared of leukemic cells in one LVL0 and five LVL-1 patients, and a significant reduction in marrow leukemic infiltrate was observed in eight of 10. No patient achieved complete remission (CR), and all died of progressive disease (n = 8) or infection (n = 2). MDR1 expression was detected by fluorescent-activated cell sorter (FACS) analysis in five of seven cases. An elevated MDR1 mRNA level was detected by quantitative polymerase chain reaction (Q-PCR) in six of eight cases studied. Clearing of leukemia cells from the marrow occurred in four of six MDR1-positive and one of three MDR1-negative patients. Despite the fact that LVL0 doses had to be reduced due to toxicity, coadministration of PSC did not produce a consistent effect on MITO PK; however, it did repeatedly lead to increased levels of VP in the serum. CONCLUSION: We conclude that PSC-MITO-VP is a tolerable regimen with antileukemic activity. Addition of PSC necessitated a 66% reduction in MITO and VP doses from a prior study without PSC.  相似文献   
94.
We have examined the formation of hydroxyphenols, nitrophenols, and the minor products 4-nitrosophenol, benzoquinone, 2,2'-biphenol, and 4,4'-biphenol from the reaction of peroxynitrite with phenol in the presence and absence of added carbonate. In the absence of added carbonate, the product yields of nitrophenols and hydroxyphenols have different pH profiles. The rates of nitration and hydroxylation also have different pH profiles and match the trends observed for the product yields. At a given pH, the sum of the rate constants for nitration and hydroxylation is nearly identical to the rate constant for the spontaneous decomposition of peroxynitrite. The reaction of peroxynitrite with phenol is zero-order in phenol, both in the presence and absence of added carbonate. In the presence of added carbonate, hydroxylation is inhibited, whereas the rate of formation and yield of nitrophenols increase. The combined maximum yield of o- and p-nitrophenols is 20 mol% (based on the initial concentration of peroxynitrite) and is about fourfold higher than the maximal yield obtained in the absence of added carbonate. The o/p ratio of nitrophenols is the same in the presence and absence of added carbonate. These results demonstrate that hydroxylation and nitration occur via two different intermediates. We suggest that the activated intermediate formed in the isomerization of peroxynitrous acid to nitrate, ONOOH*, is the hydroxylating species. We propose that intermediate 1, O=N-OO-CO2-, or secondary products derived from it, is (are) responsible for the nitration of phenol. The possible mechanisms responsible for nitration are discussed.  相似文献   
95.
Neonatal emergencies have become more common as increasingly sophisticated Neonatal Intensive Care Units graduate lower birth-weight babies born at younger gestational ages. These patients present a number of challenges to emergency physicians. They are often discharged with apnea monitors, which generate a high number of false alarms. Neonatal Intensive Care Unit graduates, however, are predisposed to a number of conditions that can result in true episodes of apnea. We present such a case and will discuss the unusual underlying cause of apnea, the utility of apnea monitors, and the need for emergency physicians to be prepared to evaluate and treat these potentially complicated patients.  相似文献   
96.
97.
98.
99.
100.
BACKGROUNDS & AIMS: Contrasting opinions exist about the pharmacological treatment of esophageal candidiasis in patients with acquired immunodeficiency syndrome (AIDS). The aim of this study was to assess the long-term efficacy of fluconazole and itraconazole treatment. METHODS: This study evaluated 2213 human immunodeficiency virus-positive patients at first episode of esophageal candidiasis diagnosed by endoscopy; 1105 received fluconazole and 1108 received itraconazole. The endoscopic and clinical response to treatment was assessed periodically until the end of the follow-up period (1 year). RESULTS: At week 2, endoscopic cure occurred in 81.2% of patients treated with fluconazole and in 65.6% of patients treated with itraconazole (P < 0.001). Clinical cure was observed in 81.5% of patients treated with fluconazole and in 75.2% of patients treated with itraconazole (P < 0.001). At the end of the follow-up period, endoscopic and clinical cure were observed in 96% of patients treated with fluconazole and in 95.6% of patients treated with itraconazole (P = 0.788), with similar differences by intention-to-treat analysis (93.6% vs. 93.3%; P = 0.853). Treatment failure was observed in 22.3% of fluconazole-treated patients and in 26.6% of itraconazole-treated patients (P = 0.022). CONCLUSIONS: Fluconazole and itraconazole are provided with good long-term therapeutic efficacy in the treatment of Candida esophagitis in patients with AIDS. Fluconazole is associated with a higher rate of cure than itraconazole in short-term treatment.  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