全文获取类型
收费全文 | 8076篇 |
免费 | 107篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 140篇 |
综合类 | 5篇 |
化学工业 | 889篇 |
金属工艺 | 112篇 |
机械仪表 | 156篇 |
建筑科学 | 167篇 |
矿业工程 | 32篇 |
能源动力 | 110篇 |
轻工业 | 704篇 |
水利工程 | 42篇 |
石油天然气 | 23篇 |
无线电 | 813篇 |
一般工业技术 | 1019篇 |
冶金工业 | 3139篇 |
原子能技术 | 113篇 |
自动化技术 | 721篇 |
出版年
2021年 | 51篇 |
2019年 | 49篇 |
2018年 | 52篇 |
2017年 | 60篇 |
2016年 | 78篇 |
2015年 | 53篇 |
2014年 | 84篇 |
2013年 | 192篇 |
2012年 | 173篇 |
2011年 | 235篇 |
2010年 | 202篇 |
2009年 | 210篇 |
2008年 | 232篇 |
2007年 | 235篇 |
2006年 | 206篇 |
2005年 | 213篇 |
2004年 | 187篇 |
2003年 | 168篇 |
2002年 | 145篇 |
2001年 | 148篇 |
2000年 | 166篇 |
1999年 | 208篇 |
1998年 | 747篇 |
1997年 | 458篇 |
1996年 | 377篇 |
1995年 | 236篇 |
1994年 | 219篇 |
1993年 | 265篇 |
1992年 | 152篇 |
1991年 | 148篇 |
1990年 | 142篇 |
1989年 | 158篇 |
1988年 | 145篇 |
1987年 | 116篇 |
1986年 | 140篇 |
1985年 | 122篇 |
1984年 | 91篇 |
1983年 | 90篇 |
1982年 | 88篇 |
1981年 | 66篇 |
1980年 | 68篇 |
1979年 | 79篇 |
1978年 | 79篇 |
1977年 | 110篇 |
1976年 | 178篇 |
1975年 | 58篇 |
1974年 | 56篇 |
1973年 | 53篇 |
1972年 | 37篇 |
1971年 | 36篇 |
排序方式: 共有8185条查询结果,搜索用时 15 毫秒
31.
32.
MC Lipman D Stobbs S Madge R Miller MA Johnson 《Canadian Metallurgical Quarterly》1998,114(1):284-290
STUDY OBJECTIVES: Asymptomatic HIV-infected individuals are increasingly recruited for studies involving invasive procedures such as bronchoscopy. We sought to determine the response to and outcome of a request for a research bronchoscopy in HIV-positive individuals with no respiratory disease, and whether this would adversely affect future decisions to have a medically indicated bronchoscopy. DESIGN AND SETTING: Prospective, semistructured, questionnaire-based study in a London teaching hospital HIV outpatient clinic. PARTICIPANTS: One hundred and seven consecutive HIV-infected eligible individuals. Thirty-one healthy volunteers served as a control group for the subjective response to bronchoscopy. MAIN OUTCOME MEASURES: Subjects' attitudes and responses to requests for bronchoscopy and subsequent behavior when they required medically indicated bronchoscopy. RESULTS: Seventy-five patients (70%) agreed to the procedure in principle, predominantly for altruistic reasons. Thirty-nine subjects underwent bronchoscopy. Five percent found it worse than expected; and 79% agreed to another research bronchoscopy (performed in 11 subjects approximately 2 years later). All patients said they would undergo bronchoscopy again for diagnostic purposes (required in seven during the study). When compared to a healthy volunteer population within the same study, postbronchoscopy symptoms were similar in frequency although somewhat different in nature. Subjects felt that a clear explanation of what was involved enhanced their participation in this research. CONCLUSIONS: Invasive research procedures such as bronchoscopy can be performed and are repeatable in a healthy HIV-infected population. Performance of procedures for research purposes does not appear to adversely affect future health-care decisions. 相似文献
33.
H. O. Menlove M. M. Fowler E. Garcia M. C. Miller M. A. Paciotti R. R. Ryan S. E. Jones 《Journal of Fusion Energy》1990,9(4):495-506
Experiments using high-efficiency neutron detectors have detected neutron emission from various forms of Pd and Ti metal in pressurized D2 gas cells and D2O electrolysis cells. Four independent neutron detectors based on3He gas tubes were used. Both random neutrons (0.05–0.2 n/s) and time-correlated neutron bursts (10–280 n) of 100-s duration were measured using time-correlation counting techniques. The majority of the neutron burst events occurred at –30°C as the samples were warming up from the liquid nitrogen temperature. 相似文献
34.
Quantitative real-time imaging of myocardium based on ultrasonic integrated backscatter 总被引:5,自引:0,他引:5
Thomas LJ Barzilai B Perez JE Sobel BE Wickline SA Miller JG 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(4):466-470
The integrated backscatter calculation over the full, two-dimensional echocardiographic sector is implemented to produce images from closed-chest dogs. This new real-time integrated backscatter measurement system allows a continuous determination of integrated backscatter from all myocardial regions in the ultrasonic view. By replacing the conventional video processor in a commercial two-dimensional echocardiographic imager with this new real-time backscatter measurement system, it is possible to produce real-time two-dimensional images based on integrated backscatter. 相似文献
35.
Three replica gratings were made from a single master; two were epoxy overcoated with different thicknesses of gold, and one was replicated directly in gold. Their performance in EUV light at grazing incidence angles was measured and compared. 相似文献
36.
Summary The MATMOD-4V-DISTORTION model has been derived [1] with the intent of improving the MATMOD-4V model by adding the capability to predict distortions of small strain offset yield surfaces. This model is compared against a variety of experimental data to verify its behavior. Model simulations are compared with experimental data for proportional and nonproportional prestress histories and the effect of yield definition is also investigated. Finally, the same model which predicts a flattening of the yield surface in
space is used to predict a rotation of the yield surface in 1-2 coordinates.With 9 Figures 相似文献
37.
38.
Conceptual fusion reactor studies over the past 10–15 yr have projected systems that may be too large, complex, and costly to be of commercial interest. One main direction for improved fusion reactors points toward smaller, higher-power-density approaches. First-order economic issues (i.e., unit direct cost and cost of electricity) are used to support the need for more compact fusion reactors. The results of a number of recent conceptual designs of reversed-field pinch, spheromak, and tokamak fusion reactors are summarized as examples of more compact approaches. While a focus has been placed on increasing the fusion-power-core mass power density beyond the minimum economic threshold of 100–200 kWe/tonne, other means by which the overall attractiveness of fusion as a long-term energy source are also addressed.Nomenclature
a
Plasma minor radius at outboard equatorial plane (m)
-
A
Plasma aspect ratioR
T
/a
-
AC
Annual charges ($/yr)
-
b
Plasma minor radius in vertical direction (m)
-
B
Magentic field at plasma or blanket (T)
-
B
c
Magnetic field at the coil (T)
-
B
Toroidal magnetic field (T)
-
B
Poloidal magnetic field (T)
- BOP
Balance of plant
-
C
Coil
-
COE
Cost of electricity (mills/kWeh)
- CRFPR
Compact RFP reactor
- CT
Compact torus (FRC or spheromak)
-
c
FPC
Unit cost of fusion power core ($/kg)
-
DC
Direct cost ($)
- DZP
Dense Z-pinch
-
E
Escalation rate (1/yr)
-
EDC
Escalation during construction ($)
- ET
Elongated tokamak
-
F
Annual fuel charges ($/yr)
-
FC
Component of UDC not strongly dependent or FPC size ($/kWe)
- FW
First wall
-
FPC
Fusion power core
-
f
Aux
Fraction of gross electric power recirculated to BOP
-
f
1
(IC+IDC+EDC)/DC
-
f
2
(O&M + SCR + F)/AC
-
IC
Indirect cost ($)
-
IDC
Interest during construction ($)
-
I
w
Neutron first-wall loading (MW/m2)
-
i
Toroidal plasma current (MA)
-
j
Plasma current density, I/a2
-
k
B
Boltzmann constant, 1.602(10)–16 (J/keV)
- LWR
Light-water (fission) reactor
-
MPD
Mass power density 1000PE/MFPC (kWe/tonne)
-
M
N
Blanket energy multiplication of 14.1-MeV neutron energy
-
M
FPC
Mass of fusion power core (tonne)
-
n
Plasma density (m–3) or toroidal MHD mode number
-
O&M
Annual operating and maintenance cost ($/yr)
-
p
f
Plant availability factor
- PFD
Poloidal field dominated (CTs, RFP, DZP)
-
P
Construction time (yr)
- PTH
Thermal power (MWt)
-
P
E
Net electric power (1-)P
ET
(MWe)
- PET
Total gross electric power (MWe)
- pf
Fusion power (MW)
-
q
Tokamak safety factor (B
/B
gq
)(a/R
T
)
-
q
e
EngineeringQ value, 1/e
-
R
T
Major toroidal radius (m)
- RFP
Reversed-field pinch
- RPE
Reactor plant equipment (Account 22)
- S
Shield
-
SCR
Annual spare component cost ($/yr)
- SSR
Second stability region for the tokamak
- S/T/H
Stellarator/torsatron/heliotron
- ST
Spherical tokamak or spherical torus
-
T
Plasma temperature (keV)
-
TDC
Total direct cost ($)
-
TOC
Total overnight cost ($)
-
UDC
Unit direct cost,TDC/10
3
P
E
($/kWe)
-
V
p
Plasma volume (m3)
-
W
p
Plasma energy (GJ)
-
W
B
Magnetic field energy (GJ)
-
Magnetic utilization efficiency, 2nkBT/(B
2/20)
-
0
Permeability of free space, 4(10)–7 H/m
-
XE
Plasma confinement efficiency, a2/4E
-
e
Plasma energy confinement time
-
p
Overall plant efficiency, TH(1-)
-
TH
Thermal conversion efficiency
-
FPC
AverageFPC mass density (tonne/m3)
-
Plasma vertical elongation factor,b/a
-
Thickness of allFPC engineering structure surround plasma (m)
-
Total recirculating power fraction, (P
ET-P
E)/P
ET, or inverse aspect ratioa/R
T
This work was performed under the auspices of USDOE, Office of Fusion Energy. 相似文献
39.
F. Martin Wilt Glenn C. Miller Richard L. Everett Murray Hackett 《Journal of chemical ecology》1993,19(2):185-194
Senescent foliage from pines is potentially a large contributor to the total monoterpene content of the litter layer, and the availability of these compounds as phytotoxins may result from release of these compounds into the vapor phase. In order to determine the fate of several monoterpene hydrocarbons in the natural environment, we examined their concentrations in fresh, senescent, and decaying needles from 32 single-leaf pinyon pine (Pinus monophylla Torr. & Frem.: Pinaceae) trees growing at two different locations. Total monoterpene content was highest in the fresh needles (mean=5.6 ± 2.2 mg/g extracted air dry weight), but also remained relatively high in senescent needles (mean=3.6 ±1.8 mg/g extracted air dry weight), either still attached to the tree or forming the freshest layer of understory litter. Decaying needles within a dark decomposing layer of litter material 5–20 cm from the surface were found to contain much lower amounts of total monoterpenes (average: =0.12 ±0.06 mg/g extracted air dry weight). Further investigation of the fate of these compounds in the pinyon understory is required to determine if these hydrocarbons are indeed exerting phytotoxic characteristics. 相似文献
40.
W. R. Miller E. W. Bell J. C. Cowan H. M. Teeter 《Journal of the American Oil Chemists' Society》1961,38(5):235-237
The reaction of dimethyl maleate and some related dienophiles with vegetable oils under pressure has been studied successfully.
When safflower oil reacts with 100% excess maleate, sulfur dioxide catalyst, and hydroquinone inhibitor at 290° for 1hr.,
80 to 90% yields of adduct fraction, based on linoleate, are obtained. Under the same conditions almost equally good yields
result with either linseed or soybean oils. With safflower oil, dimethyl fumarate gave slightly lower yields. Di-n-butyl maleate gave even poorer yields, and much residue was formed.
Paper II in a series entitled, “Reactions of Dienophiles with Vegetable Oils”. Presented at annual meeting, American Oil Chemists'
Society, St. Louis, Mo., May 1–3, 1961.
This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department
of Agriculture. 相似文献