全文获取类型
收费全文 | 5470篇 |
免费 | 107篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 303篇 |
综合类 | 13篇 |
化学工业 | 1036篇 |
金属工艺 | 127篇 |
机械仪表 | 108篇 |
建筑科学 | 81篇 |
能源动力 | 156篇 |
轻工业 | 412篇 |
水利工程 | 17篇 |
石油天然气 | 2篇 |
无线电 | 568篇 |
一般工业技术 | 882篇 |
冶金工业 | 1406篇 |
原子能技术 | 159篇 |
自动化技术 | 319篇 |
出版年
2023年 | 24篇 |
2022年 | 58篇 |
2021年 | 76篇 |
2020年 | 29篇 |
2019年 | 64篇 |
2018年 | 69篇 |
2017年 | 41篇 |
2016年 | 66篇 |
2015年 | 66篇 |
2014年 | 84篇 |
2013年 | 213篇 |
2012年 | 167篇 |
2011年 | 219篇 |
2010年 | 175篇 |
2009年 | 163篇 |
2008年 | 200篇 |
2007年 | 167篇 |
2006年 | 178篇 |
2005年 | 142篇 |
2004年 | 129篇 |
2003年 | 150篇 |
2002年 | 117篇 |
2001年 | 132篇 |
2000年 | 106篇 |
1999年 | 167篇 |
1998年 | 547篇 |
1997年 | 370篇 |
1996年 | 262篇 |
1995年 | 157篇 |
1994年 | 147篇 |
1993年 | 144篇 |
1992年 | 84篇 |
1991年 | 69篇 |
1990年 | 73篇 |
1989年 | 64篇 |
1988年 | 66篇 |
1987年 | 40篇 |
1986年 | 57篇 |
1985年 | 53篇 |
1984年 | 54篇 |
1983年 | 39篇 |
1982年 | 50篇 |
1981年 | 34篇 |
1980年 | 44篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 35篇 |
1976年 | 45篇 |
1975年 | 16篇 |
1973年 | 24篇 |
排序方式: 共有5589条查询结果,搜索用时 0 毫秒
51.
Gas exchange function through the middle ear mucosa was assessed using nitrous oxide (N2O) in patients with otitis media with effusion (OME), as well as in normal ears during elective surgery for unrelated disorders. In all normal ears except one (n = 43), an increase in pressure was observed after N2O inhalation. In 42 of 84 ears with OME, a pressure increase was observed, but not in the remaining 42 ears (50%), indicating that the gas exchange function in these latter ears was impaired. In 21 of the 42 ears showing no middle ear pressure increase following N2O inhalation, the middle ear pressure was again monitored after myringotomy and aspiration of the effusion A pressure increase was found in 16 ears, indicating that the impairment in gas exchange function in ears with OME may be reversible in most cases. Computed tomography of the mastoid was examined preoperatively in 66 ears, with the presence or absence of a middle ear pressure change well correlated in 57 ears with the presence or absence of mastoid aeration. 相似文献
52.
BACKGROUND: Major depressive disorder is often marked by repeated episodes of depression. We describe recovery from major depression across multiple mood episodes in patients with unipolar major depression at intake and examine the association of sociodemographic and clinical variables with duration of illness. METHODS: A cohort of 258 subjects treated for unipolar major depressive disorder was followed up prospectively for 10 years as part of the Collaborative Depression Study, a multicenter naturalistic study of the mood disorders. Diagnoses were made according to the Research Diagnostic Criteria, and the course of illness was assessed with the Longitudinal Interval Follow-up Evaluation. Survival analyses were used to calculate the duration of illness for the first 5 recurrent mood episodes after recovery from the index episode. RESULTS: Diagnosis remained unipolar major depressive disorder for 235 subjects (91%). The median duration of illness was 22 weeks for the first recurrent mood episode, 20 weeks for the second, 21 weeks for the third, and 19 weeks for the fourth and fifth recurrent mood episodes; the 95% confidence intervals were highly consistent. From one episode to the next, the proportion of subjects who recovered by any one time point was similar. For subjects with 2 or more recoveries, the consistency of duration of illness from one recovery to the next was low to moderate. None of the sociodemographic or clinical variables consistently predicted duration of illness. CONCLUSION: In this sample of patients treated at tertiary care centers for major depressive disorder, the duration of recurrent mood episodes was relatively uniform and averaged approximately 20 weeks. 相似文献
53.
This paper introduces the Precise Rendering Method, which generates accurately anti-aliased and highlighted images from tessellated polygons. The Precise Rendering Method first solves the aliasing problems of hidden surface removal by using the Cross Scanline Algorithm. This algorithm can exactly calculate polygon areas projected onto each pixel by using horizontal and vertical scanlines. Aliasing artifacts in shading are then prevented by the Reflection Intergration Method, which analytically integrates the intensity of reflection in the solid angle defined by surface normals at vertices of the projected area. Several synthesized images are created to show the efficiency of the Precise Rendering Method. 相似文献
54.
55.
56.
I Miura A Ohshima N Takahashi K Hashimoto T Nimura S Utsumi M Saito T Miki S Hirosawa AB Miura 《Canadian Metallurgical Quarterly》1996,64(3-4):249-256
We describe two cases of non-Hodgkin's lymphoma associated with t(3;6)(q27;p21.3) and BCL6 rearrangement. The first case was in a 78-year old woman, whose performance status (PS) was 1, the serum lactate dehydrogenase (LDH) level was elevated, and the Ann Arbor stage was IIIA with no extra nodal lymphomatous site. The pathological diagnosis from a biopsy of the inguinal lymph node was 'malignant lymphoma (ML), follicular, small cleaved' according to the Working Formulation. Complete remission was achieved. Although she had relapse in 1992, remission was obtained again. The second case was in a 62-year old man, whose PS was 1, the serum LDH was normal, and Ann Arbor stage was IVA with the involvement of the small intestine. Histological diagnosis of the cervical lymph node was 'ML, diffuse, large cell'. Complete remission was obtained without relapse. The 3q27 translocations, found in 20-30% of non-Hodgkin's lymphoma, are unique in having multiple chromosomal translocation partners. Chromosome band 6p21.3 is one of these partner sites that may be the site of a novel gene. The two cases presented here show that this translocation is a non-random chromosomal change involving 3q27 and BCL6. Since t(3;6) was the sole karyotypic abnormality in one case, this translocation may play a role in lymphomagenesis. 相似文献
57.
The biopsy specimens were homogenized and diluted ten-fold serially in Hank's solution. Each dilution samples were streaked on Skirrow's selective medium. The plates were incubated at 37 degrees C 5 to 7 days under micro-aerobic condition and counting the viable cell of H. pylori. The positive rate of specimens with H. pylori in active gastric ulcer tissue (62.0%) was higher than that in scarred tissue (51.9%). Number of H. pylori viable cells in active ulcer tissue was significantly larger than in scarred tissue. The positive correlation between Raw's gastritis score of specimens from patients with erosive gastritis and number of H. pylori viable cells was clearly noticed. 相似文献
58.
59.
This paper proposes an efficient method to develop requirement specifications for Plant Control Software (PCSW) using software-component-based prototypes. Prior to this proposal, domain analyses were conducted on existing PCSWs, and their functions were classified into “similar functions” and “individual functions”. Then PCSW Software Components (PSC: PCSW Software Component, PSCs: PCSW Software Components) were developed to correspond to these functions. PSCs as parameter-style components were developed in order to satisfy the clients’ (we define clients as owners, managers and operators of plants) requirements. A support environment for developing requirement specifications was developed. The environment consists of the Prototype Development Tool (PDT), the Behavior Check Simulator (BCS) and the Requirement Specification Development Tool (RSDT). The method consists of four steps. In the first step, PDT is used to define the parameters to customize PSCs and to compose a PCSW prototype by setting these parameters to PSCs. In the second step, BCS is used to execute the composed PCSW prototype and check its behavior and relevancy against the clients’ expectations. In the third step, steps 1 and 2 are repeated until the behavior of the PCSW prototype satisfies the clients’ requirements. Finally, a requirement specification is developed from the PCSW prototype which fully reflects the clients’ requirements. In order to evaluate the proposed method, it has been applied in five development cases. A Requirement Coverage of 91%, a Requirement Revision Rate of 6%, a PSC Reuse Rate of 92% and a LOC Reuse Rate of 83% have been achieved. In addition, a reduction of 55% in the amount of time required to develop requirement specifications has been achieved. These results indicate that the proposed method has sufficient capability to develop an exhaustive and an adequate PCSW requirement specification. And the developed PSCs have sufficient functions and capability to compose PCSW prototypes, and the support environment is capable of shortening the time taken to develop requirement specifications. 相似文献
60.