全文获取类型
收费全文 | 6922篇 |
免费 | 297篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 80篇 |
综合类 | 8篇 |
化学工业 | 1098篇 |
金属工艺 | 116篇 |
机械仪表 | 125篇 |
建筑科学 | 178篇 |
矿业工程 | 8篇 |
能源动力 | 177篇 |
轻工业 | 322篇 |
水利工程 | 32篇 |
石油天然气 | 22篇 |
无线电 | 947篇 |
一般工业技术 | 960篇 |
冶金工业 | 2241篇 |
原子能技术 | 29篇 |
自动化技术 | 898篇 |
出版年
2024年 | 9篇 |
2023年 | 95篇 |
2022年 | 176篇 |
2021年 | 276篇 |
2020年 | 215篇 |
2019年 | 180篇 |
2018年 | 221篇 |
2017年 | 186篇 |
2016年 | 273篇 |
2015年 | 167篇 |
2014年 | 224篇 |
2013年 | 352篇 |
2012年 | 264篇 |
2011年 | 298篇 |
2010年 | 218篇 |
2009年 | 212篇 |
2008年 | 210篇 |
2007年 | 186篇 |
2006年 | 142篇 |
2005年 | 127篇 |
2004年 | 101篇 |
2003年 | 89篇 |
2002年 | 75篇 |
2001年 | 82篇 |
2000年 | 53篇 |
1999年 | 105篇 |
1998年 | 740篇 |
1997年 | 366篇 |
1996年 | 280篇 |
1995年 | 186篇 |
1994年 | 139篇 |
1993年 | 171篇 |
1992年 | 55篇 |
1991年 | 66篇 |
1990年 | 47篇 |
1989年 | 70篇 |
1988年 | 58篇 |
1987年 | 52篇 |
1986年 | 55篇 |
1985年 | 39篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 32篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 67篇 |
1976年 | 132篇 |
1973年 | 8篇 |
排序方式: 共有7241条查询结果,搜索用时 15 毫秒
991.
CA Petersilge DH Witte BO Sewell E Bosch D Resnick 《Canadian Metallurgical Quarterly》1997,5(4):667-681
Transitional cell carcinoma of the bladder is associated with a high relapse rate, locally and systemically, particularly in patients with nodal or soft-tissue involvement, despite radical cystectomy. The responsiveness of the disease to chemotherapy in the metastatic setting has stimulated the use of systemic therapy in earlier stage disease, either before (neoadjuvant) or after (adjuvant) definitive local therapy. Interpretation of the data is hampered by low patient accrual to randomized trials, lack of standardization of local treatment modalities, and the use of a variety of chemotherapy agents and regimens pointing to the difficulty in reaching a consensus as to what constitutes standard therapy. In this article, we review the use of adjuvant and neoadjuvant chemotherapy, the advantages and disadvantages of both approaches, and the recommendations that can be made based on available data. New approaches to improving survival, potentially with organ preservation, include the development of more effective chemotherapy, and the identification of prognostic features-clinical or biologic-that might be a better guide to patient selection. 相似文献
992.
DA Andreychik DH Alander KM Senica ES Stauffer 《Canadian Metallurgical Quarterly》1996,78(8):1156-1166
Fifty-five patients who had sustained a burst fracture of the lumbar spine were followed for a mean of seventy-nine months (range, twenty-four to 192 months) after the injury. Thirty patients had been managed non-operatively with a short period of bed rest followed by protected mobilization. The remaining twenty-five patients had been managed operatively: eight, with posterior arthrodesis with long-segment hook-and-rod fixation; eight, with posterior arthrodesis with short-segment transpedicular fixation; six, with posterior arthrodesis and instrumentation followed by anterior decompression and arthrodesis; and three, with anterior decompression and arthrodesis. Thirty-six patients had been neurologically intact at the time of presentation and had remained so throughout the follow-up period. No neurological deterioration or symptoms of late spinal stenosis were seen. Isolated partial single-nerve-root deficits resolved regardless of the method of treatment. Patients who had had a complete single or a multiple-nerve-root paralysis seemed to have benefited from anterior decompression. Although the anatomical results as seen on the most recent radiographs were superior for the group that had been managed operatively with long posterior fixation or anterior and posterior arthrodesis, the most recent pain scores and the functional outcomes were similar for all treatment groups. At the latest follow-up evaluation, some loss of spinal alignment was noted in the patients who had been managed with short transpedicular fixation; the alignment at the most recent follow-up examination was comparable with that in the patients who had been managed non-operatively. For the patients who had had non-operative treatment, we were unable to predict the deformity at the time of follow-up on the basis of the initial diagnostic radiographs. The clinical outcome was not related to the deformity at the latest follow-up evaluation. On the basis of the results of our study, we recommend non-operative treatment for patients who do not have neurological dysfunction or who have an isolated partial nerve-root deficit at the time of presentation. For patients who have a multiple-nerve-root paralysis, anterior decompression is indicated. 相似文献
993.
The effect of the cytostatic and antiviral adenosine analogues 3-deazaadenosine (c3Ado) and 3-deaza-(+/-)-aristeromycin (c3Ari) on human skin fibroblasts was studied. Variables examined were cell morphology, viability, DNA fragmentation, expression of matrix metalloproteinases (MMPs) and matrix metalloproteinase inhibitors (TIMPs). None of these variables were changed when cells were exposed to c3Ari concentrations ranging from 10(-5) to 10(-3) M or 10(-5) M c3Ado. However, large changes in cell morphology, viability and expression of MMPs and MMP inhibitors occurred when fibroblasts were treated with 10(-4) or 10(-3) M c3Ado. Cells rounded up, shrank in volume, some detached and viability was lost without any detectable fragmentation of DNA. These changes in morphology and viability were associated with a differentiated expression of MMPs and MMP inhibitors. A large increase in collagenase activity occurred, and depending on the concentration of the adenosine analogue and the length of treatment, this change in activity could be shown to be due to one or a combination of the following factors: an increased synthesis of the collagenase protein, a decreased production of TIMP-1 or an increased activity of the collagenase superactivator, stromelysin. In contrast to this, treatment with c3Ado resulted in a decreased gelatinase activity, which in part could be attributed to an increased production of an inhibitor that seemed to affect gelatinase but not collagenase. The cellular changes induced by c3Ado seemed to reflect some of the alteration in the metabolic machinery that appears during a drug-induced or programmed/controlled death of a dermal cell. The different effects exerted by these two adenosine analogues on dermal fibroblasts can at least in part explain why c3Ado have previously been shown to be more toxic than c3Ari in animal models. 相似文献
994.
As antimicrobial resistance to tried-and-true drugs continues to build, an arsenal of new drugs aimed at resistant respiratory tract pathogens is needed. Penicillin is now ineffective against several common pathogens, including many pneumococcal organisms. Newer antimicrobials, including macrolides, cephalosporins, and fluoroquinolones, have been developed to take its place. The authors of this article present a progress report of the fight against respiratory tract infection and an assessment of the most promising newer agents for use against multidrug-resistant pathogens. 相似文献
995.
996.
An analysis of the modulation transfer noise effects from a continuous (nonbursty) digital carrier to multiple FDM/FM carriers in a common memoryless nonlinear amplifier (e.g., satellite transponder TWTA) is presented. It is shown that the modulation transfer noise, which is caused by the random envelope variations of the digital carrier due to the random data patterns and filtering of the PSK pulses, consists of both discrete and continuous spectral components in the baseband of the FDM/FM carriers. Numerical examples in terms of the noise power ratio as well as a comparison between measured and computed results are given. In general, the discrete or tonal interference component at the symbol rate of the digital carrier is quite significant. Results of this paper should be useful in the planning of FDMA satellite transponders employing the mixed PSK-FM mode of operation. 相似文献
997.
998.
Records were reviewed of 108 consecutive patients with a variety of surgically approachable malignancies undergoing scalene node biopsy as part of a preoperative staging evaluation. Metastases to the scalene nodes were detected in 12 patients (11.1%). In six patients the scalene nodes were clinically suspicious before biopsy, but in six with nonpalpable nodes the scalene metastases were occult clinically. Four of the patients with clinically benign, but pathologically positive, scalene biopsies were found among the group of 62 patients with epidermoid carcinoma of the cervix. It was concluded that routine scalene biopsies are justified in the properative evaluation of cancer patients only if the nodes are clinically suspicious, except for in patients with advanced pelvic cancers, in whom the incidence of completely occult scalene metastases is 6% or more. 相似文献
999.
Regional medical sympathectomy achieved by the intra-arterial injection of reserpine appeared to be of benefit in the treatment of five patients with acute or chronic frostbite injuries. Clinical improvement was associated with a significant increase in arteriographically determined regional perfusion. 相似文献
1000.