全文获取类型
收费全文 | 111782篇 |
免费 | 8131篇 |
国内免费 | 4192篇 |
专业分类
电工技术 | 5854篇 |
技术理论 | 11篇 |
综合类 | 6580篇 |
化学工业 | 18945篇 |
金属工艺 | 5815篇 |
机械仪表 | 6670篇 |
建筑科学 | 8626篇 |
矿业工程 | 3081篇 |
能源动力 | 3098篇 |
轻工业 | 6628篇 |
水利工程 | 1717篇 |
石油天然气 | 6216篇 |
武器工业 | 691篇 |
无线电 | 13958篇 |
一般工业技术 | 14243篇 |
冶金工业 | 5895篇 |
原子能技术 | 1238篇 |
自动化技术 | 14839篇 |
出版年
2024年 | 431篇 |
2023年 | 1749篇 |
2022年 | 2883篇 |
2021年 | 3985篇 |
2020年 | 3044篇 |
2019年 | 2584篇 |
2018年 | 2983篇 |
2017年 | 3369篇 |
2016年 | 2936篇 |
2015年 | 3855篇 |
2014年 | 4885篇 |
2013年 | 6252篇 |
2012年 | 6558篇 |
2011年 | 7180篇 |
2010年 | 6251篇 |
2009年 | 6166篇 |
2008年 | 6163篇 |
2007年 | 5754篇 |
2006年 | 6038篇 |
2005年 | 5409篇 |
2004年 | 3692篇 |
2003年 | 3196篇 |
2002年 | 2849篇 |
2001年 | 2756篇 |
2000年 | 2872篇 |
1999年 | 3379篇 |
1998年 | 2911篇 |
1997年 | 2547篇 |
1996年 | 2287篇 |
1995年 | 1921篇 |
1994年 | 1551篇 |
1993年 | 1219篇 |
1992年 | 964篇 |
1991年 | 738篇 |
1990年 | 600篇 |
1989年 | 500篇 |
1988年 | 390篇 |
1987年 | 294篇 |
1986年 | 206篇 |
1985年 | 176篇 |
1984年 | 108篇 |
1983年 | 81篇 |
1982年 | 87篇 |
1981年 | 57篇 |
1980年 | 46篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
By using a mRNA differential display technique to search for salicylate suppressible genes, we identified a cDNA in human foreskin fibroblasts, which by GenBankTM DNA data base search shows sequence homology to the recently reported cullin/Cdc53 (CUL) family genes, especially CUL-3. We have cloned the full-length human CUL-3 (Hs-CUL-3) cDNA. It encodes a 768-amino acid polypeptide and has a predicted molecular weight of 88,939. The amino acid sequence of Hs-CUL-3 shows 46% homology to that of its Caenorhabditis elegans ortholog, Ce-CUL-3, and 27 and 23% to that of Hs-CUL-1 and Hs-CUL-2, respectively. Northern blot analysis showed that phorbol 12-myristate 13-acetate increased the expression of Hs-CUL-3 mRNA in a concentration- and time-dependent manner, and this increase was inhibited by sodium salicylate. Hs-CUL-3 widely expressed in human tissues and its expression in cultured COLO205 colon cancer cells was increased when compared with that in normal colon cells. It is likely that Hs-CUL-3 is involved in cell proliferation control. 相似文献
82.
We studied 722 reexcision scars of benign and malignant lesions (except melanocytic lesions) excised over a 24-month period. The formalin-fixed, paraffin-embedded tissue sections were examined histologically and immunohistochemically. The histological features of melanocytic hyperplasia were present in 59 cases (8%), 56 from the sun-exposed skin of the face and neck and three from the trunk [p < 0.00001]. The most common sites were the nose and lower eyelids, but the forehead was also frequently involved. Of the 59 patients, 41 were women (p < 0.0001). Basal cell carcinoma was the most frequent original lesion in both sexes (80%). No melanocytic hyperplasia was found in 663 cases (298 on the trunk and extremities and 365 on the head and neck). We have seen this reaction pattern following reexcision of melanocytic lesions as well. Thus, interpreting reexcision margins when lentigo maligna or similar lesions are reexcised may be fraught with difficulty. It is important for pathologists and dermatopathologists to recognize this phenomenon because histologically the presence of increased numbers of large melanocytes could be misinterpreted as melanoma in situ. 相似文献
83.
Dielectric properties and conduction of the epoxy and its composites were measured over the temperature range — 20 to 70°C and the frequency range 10–4-10–1 Hz. Dielectric properties were obtained by performing Fouriertransforms on the charging and discharging curves. The resulting isothermal frequency spectra of dielectric constants and dielectric loss factors were analysed using the Cole-Cole law to obtain the activation energy for each material. The activation energies were also obtained for isothermal d.c. current. Current density-electric field-temperature characteristics are obtained for field levels up to 60 kV cm–1, with step excitation of the applied field and currents recorded after a delay time of 10 min. Current density and electric field were computed and plotted for constant temperature. The linear (ohmic) curves were obtained for fields up to about 60 kV cm–1 for temperatures up to about 20 °C. The non-linearity at the higher fields and temperatures did not imply the occurrence of non-ionic conduction. It has been demonstrated that both electric conduction and relaxation behaviour were ionic and could be fit by the Nakajima model for the unfilled epoxy and the Taylor model for the composites. 相似文献
84.
BOOTSTRAP CONTROL CHARTS 总被引:1,自引:0,他引:1
85.
Li Xi Zuoyan Peng Wei Fan Kui Guo Gu Jianmin Muyu Zhao Wu Guoqiang 《Materials Science and Engineering: B》1996,40(2-3):147-152
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere. 相似文献
86.
Tri-band frequency selective surface with circular ring elements 总被引:2,自引:0,他引:2
Theoretical analysis, physical reasonings, and experimental verifications are presented for a frequency selective surface with circular ring elements. Both double-screen and single-screen designs are generated for a tri-band system that reflects the X-band signal while transmitting through the S- and Ku-band signals. In these designs, the dielectric loading effect is used to reduce ring size and element spacing and thus avoid the grating lobe problem. The circular ring element is very insensitive to a large variation of the RF incident angle 相似文献
87.
含氨烷基聚硅氧烷的研究进展 总被引:1,自引:0,他引:1
对含氨烷基聚硅氧烷的研究进行综述,着重介绍含氨烷基聚硅氧烷的种类,性能特点,制备方法及应用等。 相似文献
88.
89.
The specific surface areas (A) of different clay mineral powders were measured by both the BET method and by thin layer wicking. The values of A for the BET and the wicking experiments coincided within a few percent. Thus, the simple and inexpensive thin layer wicking approach may well suffice to obtain reliable specific surface area values for most powders. From the wicking data it is also possible to obtain a rough estimate of the average particle size. 相似文献
90.
In multiple pregnancies, survival of remaining fetuses after premature death and delivery of one fetus is uncommon. We report a case of a triplet pregnancy that was reduced to twins at the 14th gestational week and then had preterm premature rupture of membranes and intrauterine fetal death of one twin at the 17th gestational week. To save the surviving fetus, delivery of the dead fetus and ligation of the umbilical cord at the cervical level were performed. We also performed McDonald cervical cerclage to keep the placenta of the dead fetus as well as that of the surviving one in the uterine cavity. After a series of aggressive procedures, including immediate administration of tocolytic agents, and antibiotic prophylaxis to prevent infection and preterm labor, the surviving fetus was delivered vaginally 73 days later due to intractable uterine contractions. After a 10-week hospital stay, the infant boy, weighing 2,500 g, was discharged without any sequelae. To our knowledge, this was the longest interval between deliveries in a triplet pregnancy reported in Taiwan. With adequate intensive management, a satisfactory outcome of the fetus and mother in such cases is possible. 相似文献