全文获取类型
收费全文 | 8872篇 |
免费 | 797篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 121篇 |
综合类 | 15篇 |
化学工业 | 2148篇 |
金属工艺 | 350篇 |
机械仪表 | 431篇 |
建筑科学 | 135篇 |
矿业工程 | 3篇 |
能源动力 | 348篇 |
轻工业 | 915篇 |
水利工程 | 35篇 |
石油天然气 | 7篇 |
武器工业 | 1篇 |
无线电 | 1522篇 |
一般工业技术 | 2105篇 |
冶金工业 | 594篇 |
原子能技术 | 83篇 |
自动化技术 | 872篇 |
出版年
2024年 | 11篇 |
2023年 | 134篇 |
2022年 | 196篇 |
2021年 | 330篇 |
2020年 | 231篇 |
2019年 | 232篇 |
2018年 | 315篇 |
2017年 | 337篇 |
2016年 | 406篇 |
2015年 | 354篇 |
2014年 | 462篇 |
2013年 | 639篇 |
2012年 | 649篇 |
2011年 | 841篇 |
2010年 | 587篇 |
2009年 | 550篇 |
2008年 | 448篇 |
2007年 | 390篇 |
2006年 | 323篇 |
2005年 | 259篇 |
2004年 | 263篇 |
2003年 | 220篇 |
2002年 | 165篇 |
2001年 | 153篇 |
2000年 | 157篇 |
1999年 | 137篇 |
1998年 | 230篇 |
1997年 | 127篇 |
1996年 | 105篇 |
1995年 | 57篇 |
1994年 | 64篇 |
1993年 | 46篇 |
1992年 | 36篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1974年 | 7篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有9685条查询结果,搜索用时 15 毫秒
971.
An one-pole-four-throw switch that can be used to switch between the band select filters of four cellular bands and a single input programmable low noise amplifier has been demonstrated in a 0.18-/spl mu/m complementary metal oxide semiconductor process. Its insertion losses are 0.39, 0.61, 0.66, and 0.75dB in the GSM900, DCS1800, PCS1900, and wide-band code division multiple access system bands. IIP3's of the switch are /spl sim/27dBm and isolations are greater than 22dB. 相似文献
972.
Don Woong Choi Jee Yeun Kim Seon Hee Choi Hee Su Jung Hyo Joo Kim So Yean Cho Chan Soon Kang Seung Yeup Chang 《Food chemistry》2006
Although it has been known that pomegranate (Punica granatum L.) contains several steroid hormones, concrete experimental proofs about that have not been published until now. In order to identify and evaluate the contents of steroid hormones including estrone in pomegranate, we analyzed pomegranate seed, fruit juice and commercial preparations. We developed a reproducible and sensitive method for separation and identification of steroid hormones in pomegranate samples using both high performance liquid chromatography (HPLC)–PDA and gas chromatography (GC)–MS. In case of HPLC, an isocratic elution method using 35% aqueous acetonitrile solution at 1.0 ml/min with photodiode-array (PDA) detection at 225 nm and 254 nm was found to optimally separate and identify the steroid hormones from the pomegranate samples with a run time of less than 30 min. The pomegranate samples were comparatively analyzed to the HPLC results by GC/FID or GC/MS detection on a HP-1 (30 m length, 0.32 mm I.D.) with helium as carrier gas under the oven temperature control as follows: start 220 °C for 5 min, raising 5 °C per min, final 280 °C for 10 min. The HPLC and GC methods were successfully applied to the identification of steroid hormones in pomegranate samples. Our results suggested that there were no steroid estrogens including estrone, estradiol and testosterone in pomegranate seed, fruit juice and preparations. Consequently, we assumed that the previously reported analysts of pomegranate were misunderstood their analytical results according to either the estrogen-like effects or similarity of peak retention time and Rf values in experiments. 相似文献
973.
974.
975.
C Renner S Ohnesorge G Held S Bauer W Jung JP Pfitzenmeier M Pfreundschuh 《Canadian Metallurgical Quarterly》1996,88(1):236-241
To investigate the mechanisms underlying the deficiency of T lymphocytes from patients with Hodgkin's disease, we investigated the expression of the T-cell receptor (TCR) zeta chain in patients with Hodgkin's disease. By flow cytometry using an anti-zeta chain monoclonal antibody, peripheral blood T lymphocytes from patients with untreated Hodgkin's disease were shown to express decreased levels of the TCR zeta chain. After stimulation by combined CD3 and CD28 cross-linking, T cells from Hodgkin's disease patients upregulated zeta chain protein expression to normal values within 48 hours and achieved a cytolytic potential and levels of interleukin (IL)-2 secretion that were not different from T cells obtained from healthy controls. These results show that downregulation of the TCR zeta chain in Hodgkin's T lymphocytes is a reversible event. Costimulation of CD3 and CD28 is a novel approach for overcoming the T-cell deficiency in Hodgkin's disease and might be exploited clinically. As upregulation of the zeta chain can also be achieved using bispecific monoclonal antibodies (BI-MoAbs) with specificity for tumor antigens and CD3 and CD28, respectively, an immunotherapy with CD3/CD30 and CD28/CD30 Bi-MoAbs may overcome and should therefore, not be jeopardized by the inherent T-cell deficiency in patients with Hodgkin's disease. 相似文献
976.
Jae-Il Jung 《Communications Magazine, IEEE》1996,34(8):112-117
The main goal of this article is to present the translation of quality of service (QoS) parameters between layers. The QoS parameters in the ATM layer and AAL are defined. This translation concept came from the QoS framework in which the influence of the protocol stack on the QoS should be considered. As an example, we concentrate on the translation from the AAL to the ATM layer, as the AAL must be designed to be service-dependent and specific. Translation, both taking the transport protocol into account as well as between application and transport QoS, needs further study. However, our study shows that the QoS translation is a possible and good approach in end-to-end QoS guarantees in the broadband integrated services digital network (B-ISDN). As far as the end-to-end QoS guarantee issue is concerned, the transport QoS requirements are specified in terms of bounds on transport QoS parameters. The bounds on transport QoS parameters will be translated into the bounds on ATM layer QoS parameters. The ATM-layer QoS parameters resulting from the translation will be the performance requirements on a connection basis for the ATM network, but are basically the end-to-end parameters, including the network and the end systems. Therefore, the QoS translation finally results in the network performance parameters in the ATM network. We define QoS parameters in the AAL and ATM layer. Case studies in which the translation method is applied to a constant bit rate (CBR) video service and data service, respectively, are also presented 相似文献
977.
The behaviors of concentric-double inclusions dispersed in continuous media are investigated theoretically to find some possibilities
of improving toughness of composite materials by dispersing double-inc’usions instead of single-inclusions. The general solutions
of the Stokes equation, expressed in terms of the spherical harmonics, are used for analyzing the problems that are related
to the concentric-double inclusions. From the analysis, it is found that the pressure and stress fields inside and outside
the inclusion can be modified by changing the modulus ratios and the thickness of shell layer. Especially, the positions of
the minimum pressure points and the maximum stress points turn out to be controllable with some degree of freedom. 相似文献
978.
J Sun AG Sheil C Wang L Wang K Rokahr A Sharland SE Jung L Li GW McCaughan GA Bishop 《Canadian Metallurgical Quarterly》1996,62(12):1725-1730
Liver allografts in some rat strains are often spontaneously accepted across a complete major histocompatibility barrier without the requirement for immunosuppression while other nonliver allografts are rejected. In previous studies, we have shown that spontaneous acceptance is dependent on liver passenger leukocytes. Depletion of passenger leukocytes by donor irradiation allows rejection, with DA recipients of irradiated PVG livers having a median survival time (MST) of 16 days. Here we show that, in this model, spontaneous acceptance is reconstituted by intravenous injection of donor leukocytes. Intravenous injection of 3-5x10(7) PVG liver leukocytes significantly prolonged DA survival time (MST=96 days, P=0.026), as did 5x10(7) spleen leukocytes (MST>100 days, P=0.002). Deletion of T cells from the reconstituting inoculum reduced survival time (MST=78 days, P=0.039), whereas deletion of B cells or monocytes/macrophages had no effect on survival time. In contrast, PVG hearts are regularly rejected by DA recipients, and PVG liver or spleen leukocytes, even at doses of greater than 3x10(8) cells/recipient, were unable to induce heart acceptance. To investigate the possibility that acceptance of the irradiated liver but not the heart might be due to the large mass of the liver, two kidneys and two hearts of PVG origin were transplanted to each DA recipient together with 1.5x10(8) PVG leukocytes. These organs survived for greater than 200 days, thereby showing that a large mass of donor tissue, in association with donor leukocytes, leads to acceptance of organs that are rejected if transplanted singly. It appears likely that spontaneous liver transplant tolerance is a high-dose or activation-associated immune phenomenon. 相似文献
979.
Because of its remarkable simplicity and the robustness of the isolated preparation, the lamprey has been used as a model system to study locomotion and its central pattern generator. The function of the spinal cord is relatively well understood in this context, but the role of the brain or even the caudal brainstem remains less so. We here present a study of the interaction between the caudal brainstem and the spinal pattern generator for locomotion. We show that the interaction is highly complex, with both feedforward input from the brainstem to spinal cord and feedback input from the spinal cord to brainstem playing a significant role in the motor output during locomotion. The brainstem, when diffusely stimulated pharmacologically, can initiate fictive locomotion, or it can disrupt or alter the ongoing D-glutamate initiated motor output. The nature of the disruptions vary greatly, and can induce generalized irregularity, while the alterations can include accelerating or decelerating of the bursting. All behaviors are displayed with spectrograms of the motor nerve discharge. We also show that the unstimulated brainstem can disrupt as well as slow the bursting, but in a complex fashion. Finally, a slow episodic behavior initiated from the caudal brainstem is also described. This can be elicited either by D-glutamate to the brainstem or by ascending activity from the spinal cord pattern generator. Thus, we demonstrate that the interaction between the brainstem and the spinal cord during the production of locomotion is highly complex. The locomotion that is exhibited by the combined brainstem-spinal cord preparation is extremely variable. This is in striking contrast to the variability of the locomotor output pharmacologically induced in the spinal cord alone. The latter preparation exhibits remarkable regularity, or upon occasion, irregularity, but not the routine irregularity or the systemic up and down changes in frequency seen with the brainstem present. However, the pattern of frequency changes induced by the brainstem is not predictable, and remains to be understood. 相似文献
980.
20 pairs of sera from the National System of Seroepidemiological Surveillance of the triple viral vaccine received in the laboratory with febrile rash diagnosis were studied. By using the hemagglutination inhibition test, it was observed an abnormal answer of antibodies to both rubella and measles through a falling of the antibody titre in one or both diseases, or in one of them with seroconversion to the other one. With the aim of defining the existence of a possible polyclonal activation already described in literature, it was decided to study the antibody response to family Herpesviridae (HSV, EBV, CMV, VZV). 80% of answer to these viruses were found. The results are submitted and discussed. 相似文献