全文获取类型
收费全文 | 97942篇 |
免费 | 545篇 |
国内免费 | 885篇 |
专业分类
99372篇 |
出版年
2021年 | 34篇 |
2019年 | 30篇 |
2018年 | 11868篇 |
2017年 | 10709篇 |
2016年 | 7506篇 |
2015年 | 685篇 |
2014年 | 415篇 |
2013年 | 812篇 |
2012年 | 4438篇 |
2011年 | 13037篇 |
2010年 | 12157篇 |
2009年 | 8362篇 |
2008年 | 10000篇 |
2007年 | 11644篇 |
2006年 | 514篇 |
2005年 | 799篇 |
2004年 | 1293篇 |
2003年 | 1270篇 |
2002年 | 1053篇 |
2001年 | 317篇 |
2000年 | 222篇 |
1999年 | 112篇 |
1998年 | 73篇 |
1997年 | 84篇 |
1996年 | 48篇 |
1995年 | 55篇 |
1994年 | 62篇 |
1993年 | 91篇 |
1992年 | 89篇 |
1991年 | 82篇 |
1990年 | 50篇 |
1989年 | 58篇 |
1988年 | 74篇 |
1987年 | 56篇 |
1986年 | 49篇 |
1985年 | 49篇 |
1984年 | 61篇 |
1983年 | 60篇 |
1982年 | 54篇 |
1981年 | 55篇 |
1980年 | 46篇 |
1979年 | 29篇 |
1978年 | 29篇 |
1977年 | 33篇 |
1976年 | 32篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1972年 | 262篇 |
1971年 | 283篇 |
1962年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Background
There is an ongoing discussion about age limits for deep brain stimulation (DBS). Current indications for DBS are tremor-dominant disorders, Parkinson's disease, and dystonia. Electrode implantation for DBS with analgesia and sedation makes surgery more comfortable, especially for elderly patients. However, the value of DBS in terms of benefit-risk ratio in this patient population is still uncertain. 相似文献992.
Baughman RP 《Arthritis research & therapy》2007,9(Z2):S8
Pulmonary involvement is common in sarcoidosis, an immune-mediated inflammatory disorder that is characterized by non-caseating granulomas in tissue. Sarcoid patients with advanced pulmonary disease, especially end-stage pulmonary fibrosis, risk developing pulmonary hypertension (World Health Organization group III pulmonary hypertension secondary to hypoxic lung disease). Increased levels of endothelin (ET)-1 in plasma and bronchoalveolar lavage of some sarcoid patients suggest that ET-1 may be driving pulmonary fibrosis and sarcoidosis-associated pulmonary hypertension. Although a relationship between raised levels of ET-1 and clinical phenotype is yet to be identified, early evidence from studies of ET-1 blockade with drugs such as bosentan is encouraging. Such therapy possibly could be combined with standard anti-inflammatory agents to improve outcome. 相似文献
993.
Transposon mediated transgenesis in a marine invertebrate chordate: <Emphasis Type="Italic">Ciona intestinalis</Emphasis> 下载免费PDF全文
Achievement of transposon mediated germline transgenesis in a basal chordate, Ciona intestinalis, is discussed. A Tc1/mariner superfamily transposon, Minos, has excision and transposition activities in Ciona. Minos enables the creation of stable transgenic lines, enhancer detection, and insertional mutagenesis. 相似文献
994.
Diwakar Aggarwal Anil Kumar M. Sudhakara Reddy 《Plant Cell, Tissue and Organ Culture》2010,102(1):45-52
An efficient shoot organogenesis system has been developed from mature plants of selected elite clones of Eucalyptus tereticornis Sm. Cultures were established using nodal explants taken from freshly coppice shoots cultured on Murashige and Skoog medium
containing 58 mM sucrose, 0.7% (w/v) agar (MS medium) and supplemented with 2.5 μM benzyladenine (BA) and 0.5 μM α-naphthaleneacetic
acid (NAA). Shoot organogenesis was achieved from leaf segments taken from elongated microshoots on MS medium supplemented
with 5.0 μM BA and 1.0 μM 2,4-dichlorophenoxyacetic acid (2,4-D). The addition of cefotaxime to the medium promoted shoot
differentiation, whereas carbenicillin and cephalexin inhibited shoot differentiation. Maximum shoot bud organogenesis (44.6%)
occurred in explants cultured on MS medium supplemented with 5.0 μM BA, 1.0 μM 2,4-D and 500 mg/l cefotaxime. Leaf maturity
influenced shoot regeneration, with maximum shoot organogeneisis (40.5%) occurring when the source of explants was the fifth
leaf (14–16 days old) from the top of microshoot. Shoot organogenic potential also varied amongst the different clones of
E. tereticornis. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) analyses indicated clonal uniformity of
the newly formed shoots/plants, and these were also found to be true-to-type. 相似文献
995.
Singapore is located near the equator, off the southern tip of the Malay Peninsula. The whole country consists mostly of lowland.
It has many interesting types of natural habitats such as primary rain forest, freshwater swamp forest, mangroves, secondary
forests, shrub, grasslands, and urban parks and fields. The climate is equatorial with relatively uniform temperature and
high humidity. Unfortunately, many of the natural habitats and the native orchids which thrive there have disappeared due
to habitat destruction. Some 226 species of native orchids have been recorded in Singapore. However, of these 178 are considered
to be extinct, and only five are common. The orchid conservation programme aims to monitor existing species, explore ways
to conserve their germplasm, and increase their numbers in natural, semi-natural, and urban environments through ex-situ seedling
culture and subsequent re-introduction into appropriate habitats, including roadside trees, parks and natural areas. In the
first phase of the programme, we have successfully propagated and carried out experiments of re-introduction on five species
of native orchids, namely, Grammatophyllum speciosum, Bulbophyllum vaginatum, Bulbophyllum membranaceum, Cymbidium finlaysonianum and Cymbidium bicolor. Survival percentages 8-yr after the reintroduction events ranged from 10 to 95 for G. speciosum, the target species of the earliest re-introduction experiments. Size of the seedlings at reintroduction, host trees, and
relative humidity seemed to play significant roles in the success rate of the reintroductions. 相似文献
996.
The European bitterling, Rhodeus amarus, is a non-indigenous fish species in British fresh waters. It lays its eggs in unionid mussels which themselves are vulnerable
to fouling by the non-indigenous zebra mussel, Dreissena polymorpha. Observations from an unmanipulated natural system showed that only 27% of zebra mussel-fouled Unio pictorum hosted bitterling, while 47% of unfouled U. pictorum hosted bitterling. We conducted a field experiment in the River Great Ouse catchment, Cambridgeshire, England in May–June
2007 and 2008 to quantify the impact of zebra mussels on bitterling load in host mussels. Zebra mussel-fouled unionids were
significantly less likely to host bitterling than unfouled unionids. The number of unionids hosting bitterling did not differ
significantly whether the zebra mussels fouling the unionid were alive or dead. Bitterling appeared to discriminate against
zebra mussel-fouled unionids less as the 2007 breeding season advanced, potentially because preferred unfouled unionids had
a higher bitterling load, and were therefore relatively lower quality hosts than at the start of the breeding season. 相似文献
997.
998.
999.
1000.
Mervi Laaksonen Kaisa Murdoch Juha Siitonen Gergely Várkonyi 《Journal of Insect Conservation》2010,14(1):89-98
The beetle genus Agathidium is the largest insect group documented that principally feeds on slime moulds. Agathidium pulchellum, one of the rarest Agathidium species in Europe, is listed in the EU’s Habitats Directive. We studied the habitat associations of A. pulchellum in 44 sites located in old-growth and managed forests in eastern Finland. Agathidium pulchellum occurred exclusively on the slime-mould species Trichia decipiens. The host was associated with mid-decayed aspen, spruce and birch logs, and its incidence grew with both increasing log diameter
and stand-level log density of spruce and aspen. We also observed that even if its host was present, the beetle was absent
from sites with less than 80 aspen and spruce logs per hectare. All sites with A. pulchellum were natural forests of high conservation value. Our results show that it is possible to systematically survey the occurrence
of A. pulchellum. 相似文献