全文获取类型
收费全文 | 151184篇 |
免费 | 5201篇 |
国内免费 | 839篇 |
出版年
2022年 | 361篇 |
2021年 | 853篇 |
2020年 | 528篇 |
2019年 | 639篇 |
2018年 | 12456篇 |
2017年 | 11263篇 |
2016年 | 8640篇 |
2015年 | 2965篇 |
2014年 | 2780篇 |
2013年 | 3608篇 |
2012年 | 8350篇 |
2011年 | 16758篇 |
2010年 | 14447篇 |
2009年 | 10491篇 |
2008年 | 13056篇 |
2007年 | 14610篇 |
2006年 | 3621篇 |
2005年 | 3898篇 |
2004年 | 4287篇 |
2003年 | 4136篇 |
2002年 | 3857篇 |
2001年 | 962篇 |
2000年 | 687篇 |
1999年 | 751篇 |
1998年 | 872篇 |
1997年 | 617篇 |
1996年 | 611篇 |
1995年 | 591篇 |
1994年 | 578篇 |
1993年 | 624篇 |
1992年 | 554篇 |
1991年 | 500篇 |
1990年 | 396篇 |
1989年 | 412篇 |
1988年 | 419篇 |
1987年 | 350篇 |
1986年 | 340篇 |
1985年 | 395篇 |
1984年 | 451篇 |
1983年 | 391篇 |
1982年 | 461篇 |
1981年 | 409篇 |
1980年 | 364篇 |
1979年 | 240篇 |
1978年 | 293篇 |
1977年 | 284篇 |
1976年 | 231篇 |
1974年 | 236篇 |
1972年 | 372篇 |
1971年 | 397篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
211.
Peter Van Bogaert Lieve Peremans Nadine Diltour Danny Van heusden Tinne Dilles Bart Van Rompaey Donna Sullivan Havens 《PloS one》2016,11(4)
The aim of the study reported in this article was to investigate staff nurses’ perceptions and experiences about structural empowerment and perceptions regarding the extent to which structural empowerment supports safe quality patient care. To address the complex needs of patients, staff nurse involvement in clinical and organizational decision-making processes within interdisciplinary care settings is crucial. A qualitative study was conducted using individual semi-structured interviews of 11 staff nurses assigned to medical or surgical units in a 600-bed university hospital in Belgium. During the study period, the hospital was going through an organizational transformation process to move from a classic hierarchical and departmental organizational structure to one that was flat and interdisciplinary. Staff nurses reported experiencing structural empowerment and they were willing to be involved in decision-making processes primarily about patient care within the context of their practice unit. However, participants were not always fully aware of the challenges and the effect of empowerment on their daily practice, the quality of care and patient safety. Ongoing hospital change initiatives supported staff nurses’ involvement in decision-making processes for certain matters but for some decisions, a classic hierarchical and departmental process still remained. Nurses perceived relatively high work demands and at times viewed empowerment as presenting additional. Staff nurses recognized the opportunities structural empowerment provided within their daily practice. Nurse managers and unit climate were seen as crucial for success while lack of time and perceived work demands were viewed as barriers to empowerment. 相似文献
212.
213.
214.
James A. Simmons Andrea Megela Simmons 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(5):585-594
Widely divergent vertebrates share a common central temporal mechanism for representing periodicities of acoustic waveform
events. In the auditory nerve, periodicities corresponding to frequencies or rates from about 10 Hz to over 1,000 Hz are extracted
from pure tones, from low-frequency complex sounds (e.g., 1st harmonic in bullfrog calls), from mid-frequency sounds with
low-frequency modulations (e.g., amplitude modulation rates in cat vocalizations), and from time intervals between high-frequency
transients (e.g., pulse-echo delay in bat sonar). Time locking of neuronal responses to periodicities from about 50 ms down
to 4 ms or less (about 20–300 Hz) is preserved in the auditory midbrain, where responses are dispersed across many neurons
with different onset latencies from 4–5 to 20–50 ms. Midbrain latency distributions are wide enough to encompass two or more
repetitions of successive acoustic events, so that responses to multiple, successive periods are ongoing simultaneously in
different midbrain neurons. These latencies have a previously unnoticed periodic temporal pattern that determines the specific
times for the dispersed on-responses. 相似文献
215.
Primož Pirih Bodo D. Wilts Doekele G. Stavenga 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(10):987-997
The males of many pierid butterflies have iridescent wings, which presumably function in intraspecific communication. The
iridescence is due to nanostructured ridges of the cover scales. We have studied the iridescence in the males of a few members
of Coliadinae, Gonepteryx aspasia, G. cleopatra, G. rhamni, and Colias croceus, and in two members of the Colotis group, Hebomoia glaucippe and Colotis regina. Imaging scatterometry demonstrated that the pigmentary colouration is diffuse whereas the structural colouration creates
a directional, line-shaped far-field radiation pattern. Angle-dependent reflectance measurements demonstrated that the directional
iridescence distinctly varies among closely related species. The species-dependent scale curvature determines the spatial
properties of the wing iridescence. Narrow beam illumination of flat scales results in a narrow far-field iridescence pattern,
but curved scales produce broadened patterns. The restricted spatial visibility of iridescence presumably plays a role in
intraspecific signalling. 相似文献
216.
217.
218.
Janine F. Bridges Peter C. Millard John F. Woodley 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,544(2):448-451
The uptake of free and liposome-entrapped 125I-labelled poly(vinylpyrrolidone) was measured in an intestinal sac preparation from adult rats. An an equal concentration of 125I-labelled poly(vinylpyrrolidone), the rate of uptake of the liposome-entrapped material was four times that of the free macromolecule. 相似文献
219.
Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for
many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly
understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets
in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through
lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass
habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass
assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly
those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that
fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances
of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh
utility as fish habitat may in some situations be linked to the proximity of available seagrass. 相似文献
220.
Marie Lipoldová Helena Havelková Jana Badalová Jarmila Vojtíšková Lei Quan Magdaléna Krulová Yahya Sohrabi Alphons P. Stassen Peter Demant 《Cancer immunology, immunotherapy : CII》2010,59(2):203-213
Low infiltration of lymphocytes into cancers is associated with poor prognosis, but the reasons why some patients exhibit
a low and others a high infiltration of tumors are unknown. Previously we mapped four loci (Lynf1–Lynf4) controlling lymphocyte infiltration of mouse lung tumors. These loci do not encode any of the molecules that are involved
in traffic of lymphocytes. Here we report a genetic relationship between these loci and the control of production of IFNγ
in allogeneic mixed lymphocyte cultures (MLC). We found that IFNγ production by lymphocytes of O20/A mice is lower than by
lymphocytes of OcB-9/Dem mice (both H2
pz
) stimulated in MLC by irradiated splenocytes of C57BL/10SnPh (H2
b
) or BALB/cHeA (H2
d
) mice, or by ConA. IFNγ production in MLCs of individual (O20 × OcB-9)F2 mice stimulated by irradiated C57BL/10 splenocytes and genotyped for microsatellite markers revealed four IFNγ-controlling
loci (Cypr4-Cypr7), each of which is closely linked with one of the four Lynf loci and with a cluster of susceptibility genes for different tumors. This suggests that inherited differences in certain
lymphocyte responses may modify their propensity to infiltrate tumors and their capacity to affect tumor growth. 相似文献