全文获取类型
收费全文 | 4602篇 |
免费 | 159篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 35篇 |
综合类 | 1篇 |
化学工业 | 566篇 |
金属工艺 | 53篇 |
机械仪表 | 58篇 |
建筑科学 | 65篇 |
矿业工程 | 1篇 |
能源动力 | 70篇 |
轻工业 | 377篇 |
水利工程 | 21篇 |
石油天然气 | 16篇 |
无线电 | 138篇 |
一般工业技术 | 408篇 |
冶金工业 | 2723篇 |
原子能技术 | 12篇 |
自动化技术 | 222篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 75篇 |
2020年 | 52篇 |
2019年 | 74篇 |
2018年 | 64篇 |
2017年 | 85篇 |
2016年 | 81篇 |
2015年 | 63篇 |
2014年 | 99篇 |
2013年 | 135篇 |
2012年 | 98篇 |
2011年 | 146篇 |
2010年 | 103篇 |
2009年 | 125篇 |
2008年 | 101篇 |
2007年 | 97篇 |
2006年 | 69篇 |
2005年 | 59篇 |
2004年 | 68篇 |
2003年 | 56篇 |
2002年 | 45篇 |
2001年 | 36篇 |
2000年 | 51篇 |
1999年 | 108篇 |
1998年 | 834篇 |
1997年 | 529篇 |
1996年 | 326篇 |
1995年 | 206篇 |
1994年 | 148篇 |
1993年 | 198篇 |
1992年 | 45篇 |
1991年 | 38篇 |
1990年 | 47篇 |
1989年 | 39篇 |
1988年 | 33篇 |
1987年 | 36篇 |
1986年 | 37篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 30篇 |
1979年 | 4篇 |
1978年 | 11篇 |
1977年 | 61篇 |
1976年 | 124篇 |
1955年 | 4篇 |
排序方式: 共有4766条查询结果,搜索用时 15 毫秒
41.
Compound LB20304 is a fluoronaphthyridone carboxylic acid with a novel pyrrolidine substituent. This drug was compared with ciprofloxacin, levofloxacin, ofloxacin, and trovafloxacin against over 800 pathogens, most from blood stream infections, by National Committee for Clinical Laboratory Standards reference methods. LB20304 was the most active agent against gram-positive species including strains observed to be resistant to other fluoroquinolones and glycopeptides. The potency of LB20304 (MIC50, 0.03 micrograms/ml) against the Enterobacteriaceae was exceeded only by that of ciprofloxacin (0.015 micrograms/ml). It has limited activity against gram-negative anaerobes. 相似文献
42.
The influence of the nicotine antagonist dihydro-beta-erythroidine (DH beta E) was examined on various behavioural effects of nicotine in rats. Motor activity was recorded in photocell cages whereas discriminative stimulus effects were examined using two-lever drug discrimination procedures with a tandem schedule of food reinforcement (n = 8 throughout). DH beta E (0.1-3.2 mg/kg) failed to antagonise the decreases in motor activity that nicotine (0.4-0.6 mg/kg) produced in experimentally naive rats, whereas mecamylamine (1.5 mg/kg) completely blocked this effect of nicotine. DH beta E (0.1-3.2 mg/kg) antagonised the increases in motor activity that nicotine (0.4 mg/kg) produced in rats with extensive previous exposure to both nicotine and the photocell apparatus. In rats trained to discriminate either 0.1 or 0.4 mg/kg nicotine from saline, DH beta E (0.1-3.2 mg/kg) blocked the discriminative stimulus effect of nicotine. The block of the discriminative effect could be reversed by increasing the dose of nicotine; DH beta E (1.6 mg/kg) shifted the dose-response curve for nicotine discrimination to the right by a factor of 9.4. In addition, nicotine in doses of 0.32-0.64 mg/kg decreased the overall rate of lever pressing but DH beta E (1.6 mg/kg) did not influence the dose-response curve for this effect. Thus, DH beta E potently blocked the locomotor activating and discriminative stimulus effects of nicotine at doses that did not antagonise its locomotor depressant and operant response rate-reducing effects. This selective blockade supports the involvement of different subtypes of nicotinic receptor in the mediation of diverse behavioural effects. Furthermore, the rightward shift of the dose-response curve for nicotine discrimination suggested a competitive mode of action for DH beta E. 相似文献
43.
O Biurrun Unzúe A Morelló Castro J Traserra Parareda 《Canadian Metallurgical Quarterly》1997,48(5):363-374
Palatopharyngeal surgery is a therapeutic option for obstructive Sleep Apnea Syndrome (OSAS). This operation is based on the assumption that the soft palate is the principal apneogenic area of the upper airways. The effectiveness of palatopharyngeal surgery and of correcting nasal obstruction (co-adjuvant factor of SAOS), when present, was evaluated. Thirty patients were selected by cephalometry for surgery (3 women, 27 men; age 45.3 +/- 7.5 years). The success rate was 60%, which justifies the inclusion of surgery as a useful option for treating SAOS. 相似文献
44.
45.
Phase transmittance RBF neural networks 总被引:1,自引:0,他引:1
Presented is a new complex valued radial basis function (RBF) neural network with phase transmittance between the input nodes and output, which makes it suitable for channel equalisation on quadrature digital modulation systems. 相似文献
46.
47.
48.
MG Narducci L Virgilio JB Engiles AM Buchberg L Billips A Facchiano CM Croce G Russo JL Rothstein 《Canadian Metallurgical Quarterly》1997,15(8):919-926
In human leukemias and lymphomas nonrandom chromosomal rearrangements cause changes in cell growth and/or survival in such a way as to promote malignancy. The detailed study of the biochemical and genetic pathways altered in human cancer requires the identification or development of models to allow the study and manipulation of cancer gene function. Recently, the breakpoint gene TCL1, involved in chromosome translocations observed mostly in mature T-cell proliferations and chronic lymphocytic leukemias (CLL), was isolated and characterized, and showed to be part of a new gene family of proteins involved in these tumors. The murine Tcl1 gene, is similar in sequence to the murine and human MTCP1 gene also involved in T cell leukemias. The murine Tcl1 gene was shown to reside on mouse chromosome 12 in a region syntenic to human chromosome 14. Furthermore, we show that the murine Tcl1 gene is expressed early in mouse embryonic development and demonstrates expression in fetal hematopoietic organs as well as in immature T and B cells. Characterization of the murine Tcl1 gene will help in developing a mouse model of CLL and would provide the best opportunity to study and decipher the role of TCL1 in malignant transformation. 相似文献
49.
50.
MA Skinner MG Schlatter SA Heifetz JL Grosfeld 《Canadian Metallurgical Quarterly》1993,128(8):849-53; discussion 853-4
OBJECTIVE: To review the clinical presentation, treatment, and outcome in a series of children with ovarian neoplasms. DESIGN: A retrospective review of the medical records in a case series of 29 girls with ovarian neoplasms. The length of follow-up ranged from 6 months to 7 1/2 years and averaged 3.0 years in the girls with malignant tumors. SETTING: The patients were treated at a large referral children's hospital. PATIENTS: Twenty-nine girls with ovarian neoplasms were treated from 1976 to 1992. The average age of the patients was 10 years and ranged from 2 to 16 years. MAIN OUTCOME MEASURES: The principal outcomes examined were mortality and surgical morbidity. RESULTS: The most common presenting symptoms for these ovarian tumors in pediatric patients included chronic abdominal pain, an abdominal mass, or distention. Three girls presented with precocious puberty or hirsutism. In 27 cases, the tumor was a primary ovarian lesion. In two patients, the ovarian mass was the presenting finding for a stage IV non-Hodgkin's lymphoma. Seventeen tumors were benign and 12 were malignant. Tumors originating from the germ-cell line predominated (n = 17). Seven of the 10 ovarian malignant neoplasms were stage I at the time of diagnosis. All but one of the girls with malignant tumors received either adjunctive radiation therapy or multiple-agent chemotherapy. Two girls with sex cord/stromal cell tumors who presented with stage I disease ultimately developed widespread metastases. Both girls with large epithelial tumors survived. All of the girls with benign tumors and seven (70%) of 10 with malignant lesions survived. CONCLUSION: Ovarian tumors are unusual lesions in the pediatric population. Unlike in adults, such neoplasms generally originate from the germ-cell line. Whereas most ovarian tumors in girls are benign, some children have malignant tumors that are very aggressive and do not respond well to adjuvant therapy. In particular, malignant sex cord/stromal cell tumors, even when they present at an early stage, may behave unpredictably. 相似文献